"Take a deep breath, (Music starts) get ready for one of the most hypnotic things you'll ever see in a science class. Have you heard that heat rises? Well, here you can see it's true for yourself. I've got some food coloring on the bottom of a plastic container, and there's a hot mug right underneath the red food coloring. As it's heated, the water rises.
But I want you to look closely and notice something else. The blue on the sides is being drawn in. You can see it better when I speed it up. Here's the thing I want you to remember: when water moves FROM one place, it doesn't leave a void behind, water from somewhere else has to move in to take its place.
That's why you can see the blue food coloring coming in from the sides. You can see it better from above. Watch that blue food coloring get drawn in. Do you see it? The hot water reaches the top and then it gets pushed to the edges by more hot water rising underneath it.
As it goes out to the edges it starts to get cool, and cool water sinks just as hot water rises, and if you watch really carefully you can see it sink, and get drawn back toward the middle. These are called convection currents, and you see them moving here in two big ovals. They're one of the major things that drive ocean currents. Especially in the deep oceans, but it's not hot water rising that drives the ocean currents, it's really cold water sinking up near the poles.
Here's a piece of ice that I froze with some blue food coloring in it so you can see how cold water sinks. As water sinks at the North Pole, for example water has to flow up from the southern regions to take it's place, and these currents travel around the globe, some of them taking a thousand years to complete their course. Understanding convection currents will help you get a grip on weather systems, and the movements of earth's continents over the eons, and even the workings of a lava lamp. If you want to try this for yourself, click on this link for the directions you'll need Thanks for watching.
(Music fades out).Putri LaksmiDecember 11, 2017AdminBandung Indonesia
"Take a deep breath, (Music starts) get ready for one of the most hypnotic things you'll ever see in a science class. Have you heard that heat rises? Well, here you can see it's true for yourself. I've got some food coloring on the bottom of a plastic container, and there's a hot mug right underneath the red food coloring. As it's heated, the water rises.
But I want you to look closely and notice something else. The blue on the sides is being drawn in. You can see it better when I speed it up. Here's the thing I want you to remember: when water moves FROM one place, it doesn't leave a void behind, water from somewhere else has to move in to take its place.
That's why you can see the blue food coloring coming in from the sides. You can see it better from above. Watch that blue food coloring get drawn in. Do you see it? The hot water reaches the top and then it gets pushed to the edges by more hot water rising underneath it.
As it goes out to the edges it starts to get cool, and cool water sinks just as hot water rises, and if you watch really carefully you can see it sink, and get drawn back toward the middle. These are called convection currents, and you see them moving here in two big ovals. They're one of the major things that drive ocean currents. Especially in the deep oceans, but it's not hot water rising that drives the ocean currents, it's really cold water sinking up near the poles.
Here's a piece of ice that I froze with some blue food coloring in it so you can see how cold water sinks. As water sinks at the North Pole, for example water has to flow up from the southern regions to take it's place, and these currents travel around the globe, some of them taking a thousand years to complete their course. Understanding convection currents will help you get a grip on weather systems, and the movements of earth's continents over the eons, and even the workings of a lava lamp. If you want to try this for yourself, click on this link for the directions you'll need Thanks for watching.
(Music fades out).
Hey friends, welcome to the youtube channel
ALL ABOUT ELECTRONICS. Today we will see the concept of current,
voltage and power in the electrical circuits. And we will see that how they are related
to each other. So, let's start with the current.
So what is current? So, in simple terms, it can be defined as
a flow of electrical charge. So, to understand the current, first of let's
see the concept of electrical charge. So if you see any atom which is the fundamental
building block of any material, it consists of three primary elements. It contains proton and neutron which resides
in the nucleus and the electron moves around the nucleus in the orbits.
Now, the electron which is moving in the outermost
orbit can be easily knocked out of the atom by applying a little bit of energy. And these electrons which are in the outermost
orbit contributes in the flow of current. So, these electrons possess a negative charge,
while proton possesses a positive charge. Neutrons have a no charge or electrically
they are neutral.
So the same polarity charges have a tendency
to move away from each other. While the opposite polarity charges have a
tendency to move towards each other. The unit of the charge is Coulomb. And it is denoted by symbol Q or q.
When we talk about the charge of electrons
sometimes it is denoted by symbol e. So 1 electron has a charge of 1.6 X 10^ -19
Coulomb. So to have one coulomb of charge, we require
4.28 X 10^18 electrons, which is the inverse of this quantity. So to have one coulomb of charge, we require
the charge of these much electrons.
So as we have understood the concept of charge,
now let's talk about the concept of current. So, let's assume that we have a piece of copper
wire. And electrons are flowing through this copper
wire. And we want to find out that how many electrons
are flowing through this copper wire.
So, let's take one reference point in this
copper wire A-A'. That is the cross section of this copper wire. And let's assume that amount of charge that
is flowing through this copper wire is 1 C. So if 1 coulomb of charge is passing through
this reference point in one second, then we can say that the current which is flowing
through this copper wire is 1 C/S.
Or 1 Ampere. So the current can be defined as a rate at
which this electrical charge is passing through this reference point. The current is defined by a unit of an ampere. And it is denoted by the symbol I.
So to understand the concept of current, let's
take an example of tap water. The amount of water flowing through te tap
depends on the rate at which water particles are coming out of this tap. The higher the rate at which particles are
coming out of the tap. More will be the water flow.
Likewise, the higher the rate at which this
electrical charge or electrons passing through this reference point, the higher will be the
flow of current. So if 5 C of charge is passing through this
reference point in one second, then we can say that the flow of current is five ampere. So to have the movement of this charge, we
require some sort of energy. So, these electrons or electrical charge will
not contribute to the flow of current unless we apply some form of energy or external force.
At room temperature, these electrons move
randomly in all direction. Because of that net motion of flow is zero. So, to get the net motion of flow, we need
to apply some form of energy. So, let's apply this energy in the form of
an external battery, which connected to this copper wire.
So because of this battery, the electrons
will be supplied to the one end of the copper wire. So, electrons which are free electrons in
this copper wire will get repelled with this negative charge which supplied by this battery. And these free electrons will move to the
other end of the copper wire. And at the other end of the copper wire, they
will get attracted to the positive terminal of the battery.
So in this way, we get a flow of electrons
from the negative to the positive direction. So the electrons in the circuit flow from
the negative to the positive terminal. But in the electrical circuits, if you see,
we generally take a flow of current from positive to the negative direction. So that is the conventinal flow of current.
So, the conventional current flows from the
positive to the negative terminal of the circuit. So as we have discussed, to get movement of
this charge we require some sort of energy. And that energy is measured in the units of
a joule. So, let's assume that we have one coulomb
of charge and to move this charge from negative to the positive terminal, we require energy.
That is one joule. So if 1 Joule of energy is required to move
1 Cof charge from negative to the positive terminal then we can say that the potential
difference between the positive and the negative terminal is 1 volt. So, that is a definition of voltage. So, the voltage can be defined as an energy
required or work done to move a unit charge from one point to the another.
So, let's say we have two points A and B.
And at point A, we have 2 C of charge. So to move a 2 C of charge from one point
A to the B, let's say we require a 2 Jouls of energy. So, voltage or potential difference between
this point A and B can be defined as 2 J/2C, that is 1 Volt. The unit of this potential difference or voltage
is VOLT.
And it is denoted by symbol V. So the higher the amount of energy required
to move a charge from one point o the another point, the higher will be the potential difference. So, let's say if 5 C of charge is at point
A and to move this charge from point A to the point B, let's say we require 50 J of
energy. So the potential difference between the points
will be 50 J/5C = 10 Volt.
So to understand this concept, let's take
one example. Let's say we have one ball on the ground. And it's weight is 100 grams. Now, we want to through this ball from the
ground to the top of this building, which is having a height of 10 meters.
So for this task, we require some energy. Let's say for this task we require energy
E1. Now in another case, we have a ball with the
same weight or mass that is 100 gram. And we want to through this ball to the top
of one building which is having a height of 20 meters.
So for that let's say we require energy E2. Now, here energy E2 will be definitely greater
than the E1. Because the height in the second case is more. So the amount of energy required in the second
case will be the more.
So, we can compare this example with the voltage. The higher the difference between the two
points or higher the height of the building, higher the amount of energy is required to
throw a ball. Likewise, the higher the potential difference
between the twp points, more amount of energy is required to move a charge from one point
to the another point. So, now let's see the concept of power in
the electrical circuits.
So the power can be defined as the rate at
which energy is supplied or consumed in the system. So this power is denoted by symbol P.
And mathematically, it can be written as E/t. That is the rate at which energy supplied
or consumed in the system. So it is defined by unit Joule / Second.
Or Watt. While in the earlier case, Voltage mathematically
can be written as V= E/Q. That is the energy required to move a unit
charge. And the current I can be defined as rate at
which electrical charge is moving from the reference point,
that is Q/t.
Now as we were talking about the power, P=
E/t. So, let's understand the concept of power
by taking one simple example. Let's say we have one coulomb of charge at
point A. We want to move this charge from point A to
the point B.
And the energy required for this task is let's
say 5 Joules. And the time required for this task is let's
say 5 seconds. So by the definition of the power, P that
is defined by the rate at which energy is consumed. That is E/t.
Now here, in this case, to move 1 coulomb
of charge, we require 5 Jouls of energy. That is 5 Joules of energy per 1 Colomb. And the time required to move this 1 Coulomb
of charge is 5 seconds, That is 5 seconds / 1 Coulomb. So the power required for this task is 5J
/ 5 seconds, that is 1 watt.
Now, let's generalize this term. Let's say we require E joules of energy to
move Q amount of charge. And the time required for this task is t. That is t seconds for Q coulomb of charge.
That is power. So we can rewrite the term like, (E/Q) * (Q/t)
So E/Q is nothing but Voltage, as voltage can be defined as the energy required to move
a unit charge. And I, that is current can be defined as the
rate at which the charge is moving. So, we can write power as a product of V*I.
So, power can be defined as a product of V*I. So this very useful relationship between the
voltage, power and the current. Now in electrical circuits, The power is either
consumed or it is been supplied. So in electrical circuits, if you see any
element is either dissipating power or supplying a power.
So, how to know that element is supplying
a power or dissipating a power. This can find out by the simple sign convention,
So we will use this sign convention, to know
whether this element is supplying energy or it is dissipating energy. So let's say we have one element,
And the voltage between the two terminal is V. So if the current is flowing out of the positive
terminal of that element then we can say that that element is supplying a power.
Or if the current is flowing into the positive
terminal of that element then we can say that that element is dissipating a power. So, let's take one example to understand it
very clearly. Let's say we have two voltage sources,
which are connected through one resistor. We have one voltage source of 5V,
and another voltage source of 3 V.
They are connected by one resistor R.
So, the current will flow from higher potential to the lower potential, like water flows from
the higher elevation to the lower elevation. So, we will have a current in a clockwise
direction. And because of the flow of current, there
will be a potential drop across this resistorR. Let's say that is Vr.
Now, lets apply a sign convention across all
elements. So across the 5 volt source, the current is
flowing out of the terminal that means, this element or this source is supplying a power. Now, let's see a resistor,
So the current is entering into the positive terminal of the resistor. So the power is dissipated across this resistor.
Now, let's see across this 3 V voltage source. So across 3 V, current is entering into the
positive terminal. So this 3 V source is also dissipating an
energy or power. So 5V is supplying energy and the resistor
and 3V voltage source is dissipating the energy or power.
So by using this sign convention method, in
any network, we can find which elements are supplying the power and which elements are
dissipating the power. So let's summarize what we have seen in this
video. We have seen the current, voltage and power
in the electrical circuits and how they are related to each other. They are related to each other by this
P= V*I relationship.
So, hope you understood what is current, voltage
and power in the electrical circuits. If you have any query or doubts please let
me know in the coment section below. If you like this video, subcribe to the channel
ALL ABOUT ELECTRONICS..Putri LaksmiDecember 10, 2017AdminBandung Indonesia
Hey friends, welcome to the youtube channel
ALL ABOUT ELECTRONICS. Today we will see the concept of current,
voltage and power in the electrical circuits. And we will see that how they are related
to each other. So, let's start with the current.
So what is current? So, in simple terms, it can be defined as
a flow of electrical charge. So, to understand the current, first of let's
see the concept of electrical charge. So if you see any atom which is the fundamental
building block of any material, it consists of three primary elements. It contains proton and neutron which resides
in the nucleus and the electron moves around the nucleus in the orbits.
Now, the electron which is moving in the outermost
orbit can be easily knocked out of the atom by applying a little bit of energy. And these electrons which are in the outermost
orbit contributes in the flow of current. So, these electrons possess a negative charge,
while proton possesses a positive charge. Neutrons have a no charge or electrically
they are neutral.
So the same polarity charges have a tendency
to move away from each other. While the opposite polarity charges have a
tendency to move towards each other. The unit of the charge is Coulomb. And it is denoted by symbol Q or q.
When we talk about the charge of electrons
sometimes it is denoted by symbol e. So 1 electron has a charge of 1.6 X 10^ -19
Coulomb. So to have one coulomb of charge, we require
4.28 X 10^18 electrons, which is the inverse of this quantity. So to have one coulomb of charge, we require
the charge of these much electrons.
So as we have understood the concept of charge,
now let's talk about the concept of current. So, let's assume that we have a piece of copper
wire. And electrons are flowing through this copper
wire. And we want to find out that how many electrons
are flowing through this copper wire.
So, let's take one reference point in this
copper wire A-A'. That is the cross section of this copper wire. And let's assume that amount of charge that
is flowing through this copper wire is 1 C. So if 1 coulomb of charge is passing through
this reference point in one second, then we can say that the current which is flowing
through this copper wire is 1 C/S.
Or 1 Ampere. So the current can be defined as a rate at
which this electrical charge is passing through this reference point. The current is defined by a unit of an ampere. And it is denoted by the symbol I.
So to understand the concept of current, let's
take an example of tap water. The amount of water flowing through te tap
depends on the rate at which water particles are coming out of this tap. The higher the rate at which particles are
coming out of the tap. More will be the water flow.
Likewise, the higher the rate at which this
electrical charge or electrons passing through this reference point, the higher will be the
flow of current. So if 5 C of charge is passing through this
reference point in one second, then we can say that the flow of current is five ampere. So to have the movement of this charge, we
require some sort of energy. So, these electrons or electrical charge will
not contribute to the flow of current unless we apply some form of energy or external force.
At room temperature, these electrons move
randomly in all direction. Because of that net motion of flow is zero. So, to get the net motion of flow, we need
to apply some form of energy. So, let's apply this energy in the form of
an external battery, which connected to this copper wire.
So because of this battery, the electrons
will be supplied to the one end of the copper wire. So, electrons which are free electrons in
this copper wire will get repelled with this negative charge which supplied by this battery. And these free electrons will move to the
other end of the copper wire. And at the other end of the copper wire, they
will get attracted to the positive terminal of the battery.
So in this way, we get a flow of electrons
from the negative to the positive direction. So the electrons in the circuit flow from
the negative to the positive terminal. But in the electrical circuits, if you see,
we generally take a flow of current from positive to the negative direction. So that is the conventinal flow of current.
So, the conventional current flows from the
positive to the negative terminal of the circuit. So as we have discussed, to get movement of
this charge we require some sort of energy. And that energy is measured in the units of
a joule. So, let's assume that we have one coulomb
of charge and to move this charge from negative to the positive terminal, we require energy.
That is one joule. So if 1 Joule of energy is required to move
1 Cof charge from negative to the positive terminal then we can say that the potential
difference between the positive and the negative terminal is 1 volt. So, that is a definition of voltage. So, the voltage can be defined as an energy
required or work done to move a unit charge from one point to the another.
So, let's say we have two points A and B.
And at point A, we have 2 C of charge. So to move a 2 C of charge from one point
A to the B, let's say we require a 2 Jouls of energy. So, voltage or potential difference between
this point A and B can be defined as 2 J/2C, that is 1 Volt. The unit of this potential difference or voltage
is VOLT.
And it is denoted by symbol V. So the higher the amount of energy required
to move a charge from one point o the another point, the higher will be the potential difference. So, let's say if 5 C of charge is at point
A and to move this charge from point A to the point B, let's say we require 50 J of
energy. So the potential difference between the points
will be 50 J/5C = 10 Volt.
So to understand this concept, let's take
one example. Let's say we have one ball on the ground. And it's weight is 100 grams. Now, we want to through this ball from the
ground to the top of this building, which is having a height of 10 meters.
So for this task, we require some energy. Let's say for this task we require energy
E1. Now in another case, we have a ball with the
same weight or mass that is 100 gram. And we want to through this ball to the top
of one building which is having a height of 20 meters.
So for that let's say we require energy E2. Now, here energy E2 will be definitely greater
than the E1. Because the height in the second case is more. So the amount of energy required in the second
case will be the more.
So, we can compare this example with the voltage. The higher the difference between the two
points or higher the height of the building, higher the amount of energy is required to
throw a ball. Likewise, the higher the potential difference
between the twp points, more amount of energy is required to move a charge from one point
to the another point. So, now let's see the concept of power in
the electrical circuits.
So the power can be defined as the rate at
which energy is supplied or consumed in the system. So this power is denoted by symbol P.
And mathematically, it can be written as E/t. That is the rate at which energy supplied
or consumed in the system. So it is defined by unit Joule / Second.
Or Watt. While in the earlier case, Voltage mathematically
can be written as V= E/Q. That is the energy required to move a unit
charge. And the current I can be defined as rate at
which electrical charge is moving from the reference point,
that is Q/t.
Now as we were talking about the power, P=
E/t. So, let's understand the concept of power
by taking one simple example. Let's say we have one coulomb of charge at
point A. We want to move this charge from point A to
the point B.
And the energy required for this task is let's
say 5 Joules. And the time required for this task is let's
say 5 seconds. So by the definition of the power, P that
is defined by the rate at which energy is consumed. That is E/t.
Now here, in this case, to move 1 coulomb
of charge, we require 5 Jouls of energy. That is 5 Joules of energy per 1 Colomb. And the time required to move this 1 Coulomb
of charge is 5 seconds, That is 5 seconds / 1 Coulomb. So the power required for this task is 5J
/ 5 seconds, that is 1 watt.
Now, let's generalize this term. Let's say we require E joules of energy to
move Q amount of charge. And the time required for this task is t. That is t seconds for Q coulomb of charge.
That is power. So we can rewrite the term like, (E/Q) * (Q/t)
So E/Q is nothing but Voltage, as voltage can be defined as the energy required to move
a unit charge. And I, that is current can be defined as the
rate at which the charge is moving. So, we can write power as a product of V*I.
So, power can be defined as a product of V*I. So this very useful relationship between the
voltage, power and the current. Now in electrical circuits, The power is either
consumed or it is been supplied. So in electrical circuits, if you see any
element is either dissipating power or supplying a power.
So, how to know that element is supplying
a power or dissipating a power. This can find out by the simple sign convention,
So we will use this sign convention, to know
whether this element is supplying energy or it is dissipating energy. So let's say we have one element,
And the voltage between the two terminal is V. So if the current is flowing out of the positive
terminal of that element then we can say that that element is supplying a power.
Or if the current is flowing into the positive
terminal of that element then we can say that that element is dissipating a power. So, let's take one example to understand it
very clearly. Let's say we have two voltage sources,
which are connected through one resistor. We have one voltage source of 5V,
and another voltage source of 3 V.
They are connected by one resistor R.
So, the current will flow from higher potential to the lower potential, like water flows from
the higher elevation to the lower elevation. So, we will have a current in a clockwise
direction. And because of the flow of current, there
will be a potential drop across this resistorR. Let's say that is Vr.
Now, lets apply a sign convention across all
elements. So across the 5 volt source, the current is
flowing out of the terminal that means, this element or this source is supplying a power. Now, let's see a resistor,
So the current is entering into the positive terminal of the resistor. So the power is dissipated across this resistor.
Now, let's see across this 3 V voltage source. So across 3 V, current is entering into the
positive terminal. So this 3 V source is also dissipating an
energy or power. So 5V is supplying energy and the resistor
and 3V voltage source is dissipating the energy or power.
So by using this sign convention method, in
any network, we can find which elements are supplying the power and which elements are
dissipating the power. So let's summarize what we have seen in this
video. We have seen the current, voltage and power
in the electrical circuits and how they are related to each other. They are related to each other by this
P= V*I relationship.
So, hope you understood what is current, voltage
and power in the electrical circuits. If you have any query or doubts please let
me know in the coment section below. If you like this video, subcribe to the channel
ALL ABOUT ELECTRONICS..
In essence, electrical substations consist of power transformers, circuit breakers, ... ... And secondary systems for protection, load control and metering. The input signals for these secondary systems are provided by the CTs and VTs ...
... Which transform the primary currents and voltages into smaller signals. High primary currents are transformed into low currents of up to 1 or 5 amps, and high primary voltages into low voltages of up to 100 or 110 volts. The protection system uses these signals to continuously scan for faults, which enables it to quickly disconnect a faulted section from the grid.
The signals are also displayed in the control room, where they provide the data used for various switching actions. They are also needed for revenue metering. The polarity of these signals is of utmost importance, as a reversed polarity would give the secondary systems a false interpretation of the energy flow. In energy metering, a false interpretation of the energy flow based on reversed polarity ...
... Would cause the utility to pay for the energy that it delivers instead of receiving revenues. Polarity faults can lead to a protection system malfunction. There can be many reasons for improper polarity: The CT might have been installed with the wrong mechanical orientation.
A CT could have an internal wiring error. A single instrument transformers secondary wires may have been crossed ... Somewhere along the way to the secondary system. The secondary wires from two of the instrument transformers in a three phase system ...
... May have been swapped. The settings in the relay, meter, or control room device may have been set incorrectly. This is why the secondary systems correct wiring has to be verified ...
... Either during substation commissioning or after a refurbishment. Primary injection is used to validate the wiring. High currents of up to about a 1000 amps can be generated by larger testing equipment.
Smaller currents of about a 100 amps can be generated by smaller and more portable test sets. When a saw tooth signal with a distinct polarity has been used for injection, a handheld device can be used to validate the polarity throughout the system From the secondary side of the CT, along the secondary wiring all the way to the last terminal. Since this test is done phase by phase, all of the potential wiring errors or phase swaps can be detected. Testers should be able to move around the substation easily.
So ideally, they need light-weight, battery-operated equipment. The process of verifying voltage signal polarity is the same thing in principle, except that voltage is applied instead. If the wiring is correct, the secondary systems should run without a problem. COMPANO 100.Putri LaksmiDecember 10, 2017AdminBandung Indonesia
In essence, electrical substations consist of power transformers, circuit breakers, ... ... And secondary systems for protection, load control and metering. The input signals for these secondary systems are provided by the CTs and VTs ...
... Which transform the primary currents and voltages into smaller signals. High primary currents are transformed into low currents of up to 1 or 5 amps, and high primary voltages into low voltages of up to 100 or 110 volts. The protection system uses these signals to continuously scan for faults, which enables it to quickly disconnect a faulted section from the grid.
The signals are also displayed in the control room, where they provide the data used for various switching actions. They are also needed for revenue metering. The polarity of these signals is of utmost importance, as a reversed polarity would give the secondary systems a false interpretation of the energy flow. In energy metering, a false interpretation of the energy flow based on reversed polarity ...
... Would cause the utility to pay for the energy that it delivers instead of receiving revenues. Polarity faults can lead to a protection system malfunction. There can be many reasons for improper polarity: The CT might have been installed with the wrong mechanical orientation.
A CT could have an internal wiring error. A single instrument transformers secondary wires may have been crossed ... Somewhere along the way to the secondary system. The secondary wires from two of the instrument transformers in a three phase system ...
... May have been swapped. The settings in the relay, meter, or control room device may have been set incorrectly. This is why the secondary systems correct wiring has to be verified ...
... Either during substation commissioning or after a refurbishment. Primary injection is used to validate the wiring. High currents of up to about a 1000 amps can be generated by larger testing equipment.
Smaller currents of about a 100 amps can be generated by smaller and more portable test sets. When a saw tooth signal with a distinct polarity has been used for injection, a handheld device can be used to validate the polarity throughout the system From the secondary side of the CT, along the secondary wiring all the way to the last terminal. Since this test is done phase by phase, all of the potential wiring errors or phase swaps can be detected. Testers should be able to move around the substation easily.
So ideally, they need light-weight, battery-operated equipment. The process of verifying voltage signal polarity is the same thing in principle, except that voltage is applied instead. If the wiring is correct, the secondary systems should run without a problem. COMPANO 100.
Most of us don't think much
about the ocean's tides. Tide goes in, tide goes out. It's just some water moving because the moon and sun are pulling on it. But those words: "just some water" hide an
incredible amount of matter, and "pulling on it" hides an
unimaginable amount of force.
And nowhere is that more obvious
than right here. I'm just north of the Arctic Circle in Norway, half an hour's drive from a town called Bod. The land here is mostly what Douglas Adams
called 'lovely crinkly edges': and this particular lovely crinkly edge
holds the Saltstraumen Maelstrom: the most powerful tidal current on the planet. And the reason it's so powerful: that way is the sea.
That way is a fjord, a tidal inlet. Twice a day here, the sea rises and falls
by about two metres, so the water level in the fjord tries to equalise. The catch is that pretty much all the water
it needs to do that, 400 million cubic metres give or take, has to go through this channel. There are other routes that it could take, but the land masses make those slow and shallow.
They're winding country roads whereas this is like a twelve-lane freeway. It's... Well, it's a perfect storm. There's a huge mass of water on both sides
providing pressure, and the channel starts wide and
steadily narrows to the centre both ways.
It's the right width, and the right shape, to create this maelstrom of whirlpools and
currents and vortices. What surprised me the most, coming here and
standing next to it, is how much it changes, moment to moment,
second to second, every little twist in the tide and the water creates a new vortex and a new boil. I had to get close enough to
stick my camera in on a long pole, and honestly? It terrified me. Tour groups can take an inflatable boat
out into the channel, and you'll see occasional fishing vessels
taking advantage of all the marine life
that gets shunted through here.
But unlike the whirpools of myth and legend,
this maelstrom isn't going to pull a modern, bouyant,
powered boat down to the depths, although a swimmer on their own would be in
a lot of trouble, and a large ship might lose control and be
dashed against the rocks. But all this force, all this water, this is just a fraction of
what's being pulled around out on the ocean. It's just here it's visible,
it's on a human scale, it's threatening, so here we pay attention to it..Putri LaksmiDecember 10, 2017AdminBandung Indonesia
Most of us don't think much
about the ocean's tides. Tide goes in, tide goes out. It's just some water moving because the moon and sun are pulling on it. But those words: "just some water" hide an
incredible amount of matter, and "pulling on it" hides an
unimaginable amount of force.
And nowhere is that more obvious
than right here. I'm just north of the Arctic Circle in Norway, half an hour's drive from a town called Bod. The land here is mostly what Douglas Adams
called 'lovely crinkly edges': and this particular lovely crinkly edge
holds the Saltstraumen Maelstrom: the most powerful tidal current on the planet. And the reason it's so powerful: that way is the sea.
That way is a fjord, a tidal inlet. Twice a day here, the sea rises and falls
by about two metres, so the water level in the fjord tries to equalise. The catch is that pretty much all the water
it needs to do that, 400 million cubic metres give or take, has to go through this channel. There are other routes that it could take, but the land masses make those slow and shallow.
They're winding country roads whereas this is like a twelve-lane freeway. It's... Well, it's a perfect storm. There's a huge mass of water on both sides
providing pressure, and the channel starts wide and
steadily narrows to the centre both ways.
It's the right width, and the right shape, to create this maelstrom of whirlpools and
currents and vortices. What surprised me the most, coming here and
standing next to it, is how much it changes, moment to moment,
second to second, every little twist in the tide and the water creates a new vortex and a new boil. I had to get close enough to
stick my camera in on a long pole, and honestly? It terrified me. Tour groups can take an inflatable boat
out into the channel, and you'll see occasional fishing vessels
taking advantage of all the marine life
that gets shunted through here.
But unlike the whirpools of myth and legend,
this maelstrom isn't going to pull a modern, bouyant,
powered boat down to the depths, although a swimmer on their own would be in
a lot of trouble, and a large ship might lose control and be
dashed against the rocks. But all this force, all this water, this is just a fraction of
what's being pulled around out on the ocean. It's just here it's visible,
it's on a human scale, it's threatening, so here we pay attention to it..
In 2011, an international team of four astronomers
were looking through telescope data when they found evidence of
something unusual: A jet of matter was producing an electric
current of 3 exa amps a quintillion amps! Thats about as much current as youd
find in a trillion lightning bolts. It was the largest electrical current ever
discovered in space. And this jet is shooting out of the center
of a galaxy two billion light years from Earth. The galaxy is called 3C303, and its in
the direction of the Botes constellation, and its about a thousand times dimmer than
Pluto is on an average day.
So, its pretty hard to see this galaxy. But just because its not very bright in
visible light, doesnt mean it isnt bright in other
wavelengths of light. 3C303 was first observed back in 1981, by a series of radio telescopes in New Mexico
called the Very Large Array. The team of researchers who discovered the
huge electrical current used that data, plus follow-up observations
taken in 2010 and 2011.
They published their findings in The Astrophysical Journal Letters in October
2011. The main thing they found was this record-breaking
current, but they also discovered something else: the
jet itself is huge. Its being pushed outward at least 150,000 light years from the center of the
galaxy meaning that this jet is longer than the Milky
Way, which is 100,000 light years across. A jet this powerful must be fueled by something
even more powerful: the supermassive black hole in the center
of the galaxy.
Most big, active galaxies have supermassive
black holes. And lots of these supermassive black holes have huge jets of matter shooting away from
them. The jets come from a thin, rotating disk around
the black hole, called the accretion disk, which is made of
gas, dust, and even doomed stars that got too close to
the black hole. All this stuff is stuck rotating around the
black hole, pulled in by its gravity.
Itll either rotate forever or eventually
be sucked in and never seen again. The matter in this disk is spun at such high
speeds, and the turbulence heats it to such high temperatures, that the atoms break down into charged plasma
particles. And thats what leads to a huge electrical
current in the jet. The charged particles create electric and
magnetic fields, which eventually force some of this plasma
into a column, and shoots it outward in the form of a jet.
These speeding charged particles create electrical
current. Lots of electrical current. Of all the active galaxies with active supermassive
black holes in their centers, only about 10% have been found to have jets
spewing out matter. But all of these jets will have electric currents
running through them.
But why is 3C303s current so astonishingly,
exceptionally, record-breakingly huge? Well, the amount of current that these jets
carry is related to the strength of the black holes
accretion disk. Some of these jets shoot out for millions
of years, and others fizzle out. 3C303s black hole jet is thought to be
so electrified because its black hole accretion disk is so
active that it has an unusually strong magnetic field, which creates a larger amount of electricity. The researchers pointed out in their paper
that this was a rare opportunity and the first direct measure of the strength
of a large jets electric current.
But as radio telescopes become more sensitive, we should be able to observe more bright jets
like this one plus whatever giant currents are running through
them. Thanks for watching this episode of SciShow
Space, and thanks especially to our patrons on Patreon who help make this show possible. If you want to help us keep making episodes
like this, just go to patreon.Com/scishow to learn more. And dont forget to go to youtube.Com/scishowspace
and subscribe!.Putri LaksmiDecember 10, 2017AdminBandung Indonesia
In 2011, an international team of four astronomers
were looking through telescope data when they found evidence of
something unusual: A jet of matter was producing an electric
current of 3 exa amps a quintillion amps! Thats about as much current as youd
find in a trillion lightning bolts. It was the largest electrical current ever
discovered in space. And this jet is shooting out of the center
of a galaxy two billion light years from Earth. The galaxy is called 3C303, and its in
the direction of the Botes constellation, and its about a thousand times dimmer than
Pluto is on an average day.
So, its pretty hard to see this galaxy. But just because its not very bright in
visible light, doesnt mean it isnt bright in other
wavelengths of light. 3C303 was first observed back in 1981, by a series of radio telescopes in New Mexico
called the Very Large Array. The team of researchers who discovered the
huge electrical current used that data, plus follow-up observations
taken in 2010 and 2011.
They published their findings in The Astrophysical Journal Letters in October
2011. The main thing they found was this record-breaking
current, but they also discovered something else: the
jet itself is huge. Its being pushed outward at least 150,000 light years from the center of the
galaxy meaning that this jet is longer than the Milky
Way, which is 100,000 light years across. A jet this powerful must be fueled by something
even more powerful: the supermassive black hole in the center
of the galaxy.
Most big, active galaxies have supermassive
black holes. And lots of these supermassive black holes have huge jets of matter shooting away from
them. The jets come from a thin, rotating disk around
the black hole, called the accretion disk, which is made of
gas, dust, and even doomed stars that got too close to
the black hole. All this stuff is stuck rotating around the
black hole, pulled in by its gravity.
Itll either rotate forever or eventually
be sucked in and never seen again. The matter in this disk is spun at such high
speeds, and the turbulence heats it to such high temperatures, that the atoms break down into charged plasma
particles. And thats what leads to a huge electrical
current in the jet. The charged particles create electric and
magnetic fields, which eventually force some of this plasma
into a column, and shoots it outward in the form of a jet.
These speeding charged particles create electrical
current. Lots of electrical current. Of all the active galaxies with active supermassive
black holes in their centers, only about 10% have been found to have jets
spewing out matter. But all of these jets will have electric currents
running through them.
But why is 3C303s current so astonishingly,
exceptionally, record-breakingly huge? Well, the amount of current that these jets
carry is related to the strength of the black holes
accretion disk. Some of these jets shoot out for millions
of years, and others fizzle out. 3C303s black hole jet is thought to be
so electrified because its black hole accretion disk is so
active that it has an unusually strong magnetic field, which creates a larger amount of electricity. The researchers pointed out in their paper
that this was a rare opportunity and the first direct measure of the strength
of a large jets electric current.
But as radio telescopes become more sensitive, we should be able to observe more bright jets
like this one plus whatever giant currents are running through
them. Thanks for watching this episode of SciShow
Space, and thanks especially to our patrons on Patreon who help make this show possible. If you want to help us keep making episodes
like this, just go to patreon.Com/scishow to learn more. And dont forget to go to youtube.Com/scishowspace
and subscribe!.
Thomas Alva Edison... Boys! I trust you brought
your check books. I'm so full of ideas, it would take
me twelve life times to execute them. I'm working on something now,
something so new that the world will never be the same.
Hello, I'm George Westinghouse. Edison's new electric system is
significantly cheaper than gas. Does that keep you up at night? There is always more to see. We are gonna be big, big! Edison says he's months
away from lighting up the world.
Stoves, washing machines,
electric carriages... I could do the same thing with
electricity that I do with gas. Westinghouse Electric Company. Edison Electric.
It has to be! Are you rich? At the moment... Vultures in every adventure... ...Gotta keep them away. This is what he thinks of you.
Don't let him agitate you...
This is how he is. Sue him! Westinghouse Electric shall endure. He's a parasite.
His current kills people. Only because you said it would.
Mr. Edison... If you say something about me
or my company again I would ask that you tell the truth. Automation, transportation, communication...
...The man that controls that current... ...Controls that future! Though he may be unfamiliar to you, his studies have demonstrated
an understanding of electrical matters, unlike anyone I have ever known. Gentlemen and lady, Nikola Tesla. - So, what's your trade?
- I fix problems for idiots..Putri LaksmiDecember 10, 2017AdminBandung Indonesia
Thomas Alva Edison... Boys! I trust you brought
your check books. I'm so full of ideas, it would take
me twelve life times to execute them. I'm working on something now,
something so new that the world will never be the same.
Hello, I'm George Westinghouse. Edison's new electric system is
significantly cheaper than gas. Does that keep you up at night? There is always more to see. We are gonna be big, big! Edison says he's months
away from lighting up the world.
Stoves, washing machines,
electric carriages... I could do the same thing with
electricity that I do with gas. Westinghouse Electric Company. Edison Electric.
It has to be! Are you rich? At the moment... Vultures in every adventure... ...Gotta keep them away. This is what he thinks of you.
Don't let him agitate you...
This is how he is. Sue him! Westinghouse Electric shall endure. He's a parasite.
His current kills people. Only because you said it would.
Mr. Edison... If you say something about me
or my company again I would ask that you tell the truth. Automation, transportation, communication...
...The man that controls that current... ...Controls that future! Though he may be unfamiliar to you, his studies have demonstrated
an understanding of electrical matters, unlike anyone I have ever known. Gentlemen and lady, Nikola Tesla. - So, what's your trade?
- I fix problems for idiots..
If you've been invested in manga or anime for any length of time Chances are, you've at some point fallen in love with a title from Shonen Jump The now legendary publication first began in 1968 and since then has consistently published titles both widely popular and critically acclaimed One such title was 2008's meta-fictional Bakuman A series about a young artist-writer duo trying to get their manga published in a fictional version of Shonen Jump while the actual manga itself was published in Shonen Jump in real life It gave a fascinating inside into how the legendary publication worked as each of the character fight for the number 1 spot in the Shonen Jump Weekly Popularity Polls which was a survey sent out to the readers of Jump, asking to rate their favorite titles from best to worst With popular series regularly receiving anime adaptation, featured films, and merchandise while those that scored low quickly disappearing from its pages While Bakuman ended in 2012, the same weekly war still takes place in Shonen Jump today and after re-reading a little Bakuman recently I've been wondering: What are the popular titles in Jump right now? And how is the magazine itself doing? In other words, what is the current state of Shonen Jump The best place we could start with this question is with our old friend, the Shonen Jump ranking data If you'd like to see a full breakdown on how I came to these figures, just go to my following Bleach video But suffice to say, it's a pretty arduous task involving a lot of numbers and spreadsheets based of the previously mentioned ranking of the Shonen Jump titles as seen in their index This graph represents the performance of Shonen Jump top 10 manga in 2016 and if we average them out of the course of the year, we got a list that looks a little like this At number 10, we have World Trigger. A sci-fi battle series which I have not yet have a chance to read But it's apparently pretty good but was also unfortunately the subject of a pretty lackluster anime adaptation Number 9 is the Disastrous Life of Saiki K. A gag manga about a high-schooler with psychic powers trying and failing to live a normal life At number 8, we have Samon-kun wa Summoner A gag/vaguely action-oriented series about a highschool boy adept at summoning demons and tormenting his friends In at number 7, we have Food Wars. A rather beautifully illustrated battle/cooking manga with an extreme penchant for fanservice In at number 6, we have Hanamaru Zumo I've only had the chance to read the first couple of chapters in this one, but what really stands out is the spectacular artwork really making the sumo matches feel like intense, desperate struggles Coming in at number 5, we have the Promised Neverland which chronicles the life of a group of young children growing up in an orphanage, where things are...
Really bad. There's some bad things going on in that orphanage I'm currently up to date with this series, and I'm kinda in two minds about it The plot set-up is really strong, but the characters feel, well, a little flat and the art ranges from absolutely stellar, to pretty weak and inconsistent But this is also one of the freshest and newest feeling manga starting mid-2016 and as you can tell by the rank, it's quickly building in popularity Coming in at number 4 is Jump's premiere, beautiful-boys-doing-things-well manga, volleyball edition: Haikyuu Number 3 is a relatively newcomer starting in 2015 and it is the story of Black Clover For what I've read, this feels like a totally serviceable battle manga The main character's fun and the artwork is decent But it also has the air of a series heavily influenced by its contemporaries and whether it's going to be able to raise above that and carved out an identity on its own... Remains to be seen At number 2, we have Boku no Hero Academia Following the life of Deku, a boy born without superpower in a world of superheroes only to have that power mysteriously bestowed on him by his hero, All Might I'm going to leave my personal thoughts on this series for another day, but the artwork is godamn spectacular and I think that, combined with its clever premise does a lot to account for the monstrous rise of this series and shockingly, One Piece dominates the number 1 spot for its tenth year in a row I've already talked about One Piece a lot in the previous video and I'm planning on doing so again in the future upload But for now, all you really need to know is it's still the reigning king of Shonen storytelling And so business is usual for Weekly Shonen Jump, right? Well... Kind of The last 2 odd years have seen some rather unusual occurrences take place within Jump For one, two thirds of the once legendary big three are no longer in publication, leaving only One Piece And that's not the only thing that makes it feel like something is very much afoot in the weekly magazine If we returned to our yearly chart, we can see several examples of once popular series that seems to be under decline while newer ones seemed to be gaining popularity And not only that, but long standing titles like Toriko and Gintama didn't even make it into the yearly top 10, holding a rank of 12 and 14 respectively Even more curious, Toriko actually ended in volume of 51 of Jump making it one of the 9 other titles cancelled or concluded in 2016 which isn't an especially a high amount by itself but what's unusual isn't the amount of manga being cancelled but the type of manga, long running series that were once considered a mainstay in the magazine Toriko, Nisekoi, Bleach, Assassination Classroom, and possibly most notably: This is the Police Station in front of Kameari Park in Katsushika Ward A title that had been running for 40 years All mainstays at one point in their run...
Now gone And so what's going on at Jump? Well, the problem with using just ranking data to try and answer this question is two-fold For one, we are basically just taking Jump's worth on these figures while we have no real reason to suspect that Shonen Jump would fabricate these numbers there's also zero transparency to if the actual ranking shown in their index accurately reflects the surveys And second's, they can only really tell us how well a Jump manga is doing within the context of the magazine itself and so I decided to start doing a little bit of research outside Jump, namely with things like circulation and sales figures And when I did, things started to become a little clearer and what I came back to... Was One Piece Here are One Piece's sales in 2010, and here they are in 2016 And as you can see, there's a massive decline of 20 million units sold In fact, in 2014 One Piece dropped to 11.8 Million meaning that Attack on Titan that year came a paltry 150,000 units within outselling One Piece which would have been the first time a series had done so in 7 years On top of this, if we compare the top 10 manga sales of 2010 to 2016 respectively we can see a drop in a round 20 million units sold which can be entirely accounted for in the drop in One Piece's sales alone which means, manga in general are selling as much as they ever have but One Piece is in decline and if One Piece is in decline, so to is Shonen Jump And backing this up is Shonen Jump circulation has dropped from 2.9 Million units in 2010, to 2.1 In 2016 And if this trend were to continue, Shonen Jump could risk losing its place at top of the world of manga And this is the reason why they've been so decisive in cancelling and concluding so many old series Shonen Jump doesn't need old series to perform well it needs new ones to perform exceptionally which is why in the first quarter of 2017... Jump started six brand new series That's double the amount for the same period in 2015, and triple for that period in 2016 And so to round up our assessment of Weekly Shonen Jump, let's take a brief look at these 6 new titles The first of these new series is Dr. Stone The world suffers a bizarre catastrophe in which the earth's population is turned into stone Our protagonist, Taiju awakens thousands of years in the future alone except for his genius scientist friend, Senkuu Together, the two find a very limited way to unpetrified people and must carefully choose who to bring back in order to help them restart human civilization which goes well until they restore what is essentially a cross between Jesus Christ and Hannibal Lecter It's got quite a distinctive well-drawn art style, which I think takes a little getting used to but once you do, it really infused this series with a bold energy The good: strong, well executed premise with unique artwork and a great villain The bad: characters feel a little flat Hungry Marie A gender-swapping romance action series in which a highschool student is...
*Sighs* possessed by the former queen of France, Marie Theresa Charlotte and body swapping ensues It's a little more complicated than that, but honestly I find it hard to talk about much of anything given the extremely poor construction of this manga If you want to see a near perfect example of how not to layout a page, this is it Reading it is a messy frustrating chore, and not helping matters is an uninspired premise some weak character writing, and some really lackluster art Positive: If you squint, it kinda looks like a martial arts Yuri Negative: terrible page layout and Ranma already exists Robot x Laserbeam Golf is really lame Everyone knows it. We can all accept it, it's fine But it's also the subject of the misleadingly titled Robot x Laserbeam A story about a highschooler nicknamed 'robot' with the uncanny talent to hit ball with a precision of a laser I say this without a hint of mockery or ridicule, but our protagonist here is heavily implied to have either autism or asperger's syndrome And this really works into the series advantage, as his extreme natural talent at golf is only surpassed with his complete indifferent to it and the world surround him They can create some really humorous endearing character writing And it's a lot of fun watching Robot slowly warms up to the game It's well drawn, it's well laid out, and it actually kind of makes me give a shit about golf and that fact alone means it deserved a lot of credit The upside: unique, likeable main character, well put together, manages to make gold seems interesting The downside: ... GOLF! U19 After reading the first three chapters, it's difficult to even really get into what exactly U19 is about Set in the fictional future of 2036, where adults rule the worlds? It's a dystopian love story where people are genetically tested to determine their lot in life and when our main character, Kudo's girlfriend is deemed a triple S rank She's taken away which causes him to develop a different set of genetic, which leads him to having a sewing-related superpowers and becoming entangled with a group of teenage terrorist who wants to kidnap Japanese Prime Minister... *Sighs* Nothing about U19 is aggressively bad, but it just doesn't really come together in a way that feels coherent And this inherent lack of focus can be seen in everything, from the difficult to understand premise to the busy, cluttered page layouts Not terrible by any means, but pretty difficult to recommend Plus: some of the romance is conveyed pretty okay, and there's some touching moments in there Minus: cluttered, unfocused feel, lackluster character designs We Can't Study Ogata is a genius at mathematics and Furuhashi is a genius at literature The only problem is that they both want to attend college in the areas that the other one is good at And so it's down to the main character, Yuiga to tutor them both in their weaknesses to help them get into the college of their choice Despite how contrive the premise might seems, I actually find myself really enjoying this one The first couple of chapters do a great job of establishing the three main characters And the artwork has a consistently beautiful, polished feel to it And this helps pushing it beyond the average highschool romance Strengths: beautiful artwork, endearing characters Weakness: a hair-breath of becoming a very typical harem affair Demon Prince Poro's Diaries At the time of writing, there was only 1 chapter of Demon Prince available So it's still early days, but my initial impression is that, it's pretty okay Telling the story of the titularly young demon prince, who wishes to escape the barbaric ways of his violent demon home world and pursues the life of a regular highschooler There's a nice, varied quality of the artwork, and overall the first chapter was a pleasant to read But honestly, there's just isn't enough of it out to form a solid opinion, but that's it I think you can definitely do worse, and I'm interested to see where it goes Heaven: some solid gags, nice range of art styles, simple, well-executed premise Hell: so far it feels maybe a little standard And so with all these in mind, what is the current state of Shonen Jump? Well, despite some of the issues we've talked about, it's hard not to see Jump's position as anything but positive While circulation and sales of its primary products are down the fact is, that they're still light-years ahead of its competitors And with fresh new title like My Hero Academia quickly becoming sales juggernaut it's difficult to really paint the company in a negative light While I think it's always sad to see classic series disappeared from its pages, I also have to respect the drive to invest in new series Titles like the Promised Neverland and Dr.
Stone feel fresh in a way that Jump titles haven't for years and I'll be very curious to see how both series do in the coming months Whether this new approach will actually pay off or not, remains to be seen, but I think suffice to say the next year in Jump... Is going to be an interesting one Friends, thank you for joining me today I want to apologize if the sound for this episode is a little rough I'm working off a new machine, and there's been some tedious problem with the audio but it's all sorted now and it won't be an issue for future uploads I want to give a special thank you to everyone who's been supporting me on Patreon You guys are the absolute best, and the entire reason I can do this If you too would like to help support the channel then consider heading over to Patreon.Com/supereyepatchwolf I'll be back soon with another video, but in the meantime why not come hangout at the Let's Fight A Boss video game podcast We're going to talking about Hunter x Hunter, Near, and many, many other things or you can come check me down on Twitter, @eyepatchwolf Friends, take care of yourselves, and I'll see you next time.Putri LaksmiDecember 10, 2017AdminBandung Indonesia
If you've been invested in manga or anime for any length of time Chances are, you've at some point fallen in love with a title from Shonen Jump The now legendary publication first began in 1968 and since then has consistently published titles both widely popular and critically acclaimed One such title was 2008's meta-fictional Bakuman A series about a young artist-writer duo trying to get their manga published in a fictional version of Shonen Jump while the actual manga itself was published in Shonen Jump in real life It gave a fascinating inside into how the legendary publication worked as each of the character fight for the number 1 spot in the Shonen Jump Weekly Popularity Polls which was a survey sent out to the readers of Jump, asking to rate their favorite titles from best to worst With popular series regularly receiving anime adaptation, featured films, and merchandise while those that scored low quickly disappearing from its pages While Bakuman ended in 2012, the same weekly war still takes place in Shonen Jump today and after re-reading a little Bakuman recently I've been wondering: What are the popular titles in Jump right now? And how is the magazine itself doing? In other words, what is the current state of Shonen Jump The best place we could start with this question is with our old friend, the Shonen Jump ranking data If you'd like to see a full breakdown on how I came to these figures, just go to my following Bleach video But suffice to say, it's a pretty arduous task involving a lot of numbers and spreadsheets based of the previously mentioned ranking of the Shonen Jump titles as seen in their index This graph represents the performance of Shonen Jump top 10 manga in 2016 and if we average them out of the course of the year, we got a list that looks a little like this At number 10, we have World Trigger. A sci-fi battle series which I have not yet have a chance to read But it's apparently pretty good but was also unfortunately the subject of a pretty lackluster anime adaptation Number 9 is the Disastrous Life of Saiki K. A gag manga about a high-schooler with psychic powers trying and failing to live a normal life At number 8, we have Samon-kun wa Summoner A gag/vaguely action-oriented series about a highschool boy adept at summoning demons and tormenting his friends In at number 7, we have Food Wars. A rather beautifully illustrated battle/cooking manga with an extreme penchant for fanservice In at number 6, we have Hanamaru Zumo I've only had the chance to read the first couple of chapters in this one, but what really stands out is the spectacular artwork really making the sumo matches feel like intense, desperate struggles Coming in at number 5, we have the Promised Neverland which chronicles the life of a group of young children growing up in an orphanage, where things are...
Really bad. There's some bad things going on in that orphanage I'm currently up to date with this series, and I'm kinda in two minds about it The plot set-up is really strong, but the characters feel, well, a little flat and the art ranges from absolutely stellar, to pretty weak and inconsistent But this is also one of the freshest and newest feeling manga starting mid-2016 and as you can tell by the rank, it's quickly building in popularity Coming in at number 4 is Jump's premiere, beautiful-boys-doing-things-well manga, volleyball edition: Haikyuu Number 3 is a relatively newcomer starting in 2015 and it is the story of Black Clover For what I've read, this feels like a totally serviceable battle manga The main character's fun and the artwork is decent But it also has the air of a series heavily influenced by its contemporaries and whether it's going to be able to raise above that and carved out an identity on its own... Remains to be seen At number 2, we have Boku no Hero Academia Following the life of Deku, a boy born without superpower in a world of superheroes only to have that power mysteriously bestowed on him by his hero, All Might I'm going to leave my personal thoughts on this series for another day, but the artwork is godamn spectacular and I think that, combined with its clever premise does a lot to account for the monstrous rise of this series and shockingly, One Piece dominates the number 1 spot for its tenth year in a row I've already talked about One Piece a lot in the previous video and I'm planning on doing so again in the future upload But for now, all you really need to know is it's still the reigning king of Shonen storytelling And so business is usual for Weekly Shonen Jump, right? Well... Kind of The last 2 odd years have seen some rather unusual occurrences take place within Jump For one, two thirds of the once legendary big three are no longer in publication, leaving only One Piece And that's not the only thing that makes it feel like something is very much afoot in the weekly magazine If we returned to our yearly chart, we can see several examples of once popular series that seems to be under decline while newer ones seemed to be gaining popularity And not only that, but long standing titles like Toriko and Gintama didn't even make it into the yearly top 10, holding a rank of 12 and 14 respectively Even more curious, Toriko actually ended in volume of 51 of Jump making it one of the 9 other titles cancelled or concluded in 2016 which isn't an especially a high amount by itself but what's unusual isn't the amount of manga being cancelled but the type of manga, long running series that were once considered a mainstay in the magazine Toriko, Nisekoi, Bleach, Assassination Classroom, and possibly most notably: This is the Police Station in front of Kameari Park in Katsushika Ward A title that had been running for 40 years All mainstays at one point in their run...
Now gone And so what's going on at Jump? Well, the problem with using just ranking data to try and answer this question is two-fold For one, we are basically just taking Jump's worth on these figures while we have no real reason to suspect that Shonen Jump would fabricate these numbers there's also zero transparency to if the actual ranking shown in their index accurately reflects the surveys And second's, they can only really tell us how well a Jump manga is doing within the context of the magazine itself and so I decided to start doing a little bit of research outside Jump, namely with things like circulation and sales figures And when I did, things started to become a little clearer and what I came back to... Was One Piece Here are One Piece's sales in 2010, and here they are in 2016 And as you can see, there's a massive decline of 20 million units sold In fact, in 2014 One Piece dropped to 11.8 Million meaning that Attack on Titan that year came a paltry 150,000 units within outselling One Piece which would have been the first time a series had done so in 7 years On top of this, if we compare the top 10 manga sales of 2010 to 2016 respectively we can see a drop in a round 20 million units sold which can be entirely accounted for in the drop in One Piece's sales alone which means, manga in general are selling as much as they ever have but One Piece is in decline and if One Piece is in decline, so to is Shonen Jump And backing this up is Shonen Jump circulation has dropped from 2.9 Million units in 2010, to 2.1 In 2016 And if this trend were to continue, Shonen Jump could risk losing its place at top of the world of manga And this is the reason why they've been so decisive in cancelling and concluding so many old series Shonen Jump doesn't need old series to perform well it needs new ones to perform exceptionally which is why in the first quarter of 2017... Jump started six brand new series That's double the amount for the same period in 2015, and triple for that period in 2016 And so to round up our assessment of Weekly Shonen Jump, let's take a brief look at these 6 new titles The first of these new series is Dr. Stone The world suffers a bizarre catastrophe in which the earth's population is turned into stone Our protagonist, Taiju awakens thousands of years in the future alone except for his genius scientist friend, Senkuu Together, the two find a very limited way to unpetrified people and must carefully choose who to bring back in order to help them restart human civilization which goes well until they restore what is essentially a cross between Jesus Christ and Hannibal Lecter It's got quite a distinctive well-drawn art style, which I think takes a little getting used to but once you do, it really infused this series with a bold energy The good: strong, well executed premise with unique artwork and a great villain The bad: characters feel a little flat Hungry Marie A gender-swapping romance action series in which a highschool student is...
*Sighs* possessed by the former queen of France, Marie Theresa Charlotte and body swapping ensues It's a little more complicated than that, but honestly I find it hard to talk about much of anything given the extremely poor construction of this manga If you want to see a near perfect example of how not to layout a page, this is it Reading it is a messy frustrating chore, and not helping matters is an uninspired premise some weak character writing, and some really lackluster art Positive: If you squint, it kinda looks like a martial arts Yuri Negative: terrible page layout and Ranma already exists Robot x Laserbeam Golf is really lame Everyone knows it. We can all accept it, it's fine But it's also the subject of the misleadingly titled Robot x Laserbeam A story about a highschooler nicknamed 'robot' with the uncanny talent to hit ball with a precision of a laser I say this without a hint of mockery or ridicule, but our protagonist here is heavily implied to have either autism or asperger's syndrome And this really works into the series advantage, as his extreme natural talent at golf is only surpassed with his complete indifferent to it and the world surround him They can create some really humorous endearing character writing And it's a lot of fun watching Robot slowly warms up to the game It's well drawn, it's well laid out, and it actually kind of makes me give a shit about golf and that fact alone means it deserved a lot of credit The upside: unique, likeable main character, well put together, manages to make gold seems interesting The downside: ... GOLF! U19 After reading the first three chapters, it's difficult to even really get into what exactly U19 is about Set in the fictional future of 2036, where adults rule the worlds? It's a dystopian love story where people are genetically tested to determine their lot in life and when our main character, Kudo's girlfriend is deemed a triple S rank She's taken away which causes him to develop a different set of genetic, which leads him to having a sewing-related superpowers and becoming entangled with a group of teenage terrorist who wants to kidnap Japanese Prime Minister... *Sighs* Nothing about U19 is aggressively bad, but it just doesn't really come together in a way that feels coherent And this inherent lack of focus can be seen in everything, from the difficult to understand premise to the busy, cluttered page layouts Not terrible by any means, but pretty difficult to recommend Plus: some of the romance is conveyed pretty okay, and there's some touching moments in there Minus: cluttered, unfocused feel, lackluster character designs We Can't Study Ogata is a genius at mathematics and Furuhashi is a genius at literature The only problem is that they both want to attend college in the areas that the other one is good at And so it's down to the main character, Yuiga to tutor them both in their weaknesses to help them get into the college of their choice Despite how contrive the premise might seems, I actually find myself really enjoying this one The first couple of chapters do a great job of establishing the three main characters And the artwork has a consistently beautiful, polished feel to it And this helps pushing it beyond the average highschool romance Strengths: beautiful artwork, endearing characters Weakness: a hair-breath of becoming a very typical harem affair Demon Prince Poro's Diaries At the time of writing, there was only 1 chapter of Demon Prince available So it's still early days, but my initial impression is that, it's pretty okay Telling the story of the titularly young demon prince, who wishes to escape the barbaric ways of his violent demon home world and pursues the life of a regular highschooler There's a nice, varied quality of the artwork, and overall the first chapter was a pleasant to read But honestly, there's just isn't enough of it out to form a solid opinion, but that's it I think you can definitely do worse, and I'm interested to see where it goes Heaven: some solid gags, nice range of art styles, simple, well-executed premise Hell: so far it feels maybe a little standard And so with all these in mind, what is the current state of Shonen Jump? Well, despite some of the issues we've talked about, it's hard not to see Jump's position as anything but positive While circulation and sales of its primary products are down the fact is, that they're still light-years ahead of its competitors And with fresh new title like My Hero Academia quickly becoming sales juggernaut it's difficult to really paint the company in a negative light While I think it's always sad to see classic series disappeared from its pages, I also have to respect the drive to invest in new series Titles like the Promised Neverland and Dr.
Stone feel fresh in a way that Jump titles haven't for years and I'll be very curious to see how both series do in the coming months Whether this new approach will actually pay off or not, remains to be seen, but I think suffice to say the next year in Jump... Is going to be an interesting one Friends, thank you for joining me today I want to apologize if the sound for this episode is a little rough I'm working off a new machine, and there's been some tedious problem with the audio but it's all sorted now and it won't be an issue for future uploads I want to give a special thank you to everyone who's been supporting me on Patreon You guys are the absolute best, and the entire reason I can do this If you too would like to help support the channel then consider heading over to Patreon.Com/supereyepatchwolf I'll be back soon with another video, but in the meantime why not come hangout at the Let's Fight A Boss video game podcast We're going to talking about Hunter x Hunter, Near, and many, many other things or you can come check me down on Twitter, @eyepatchwolf Friends, take care of yourselves, and I'll see you next time.
The allure of sun, sand and the ocean are synonymous with summer. The beach can provide us with a calm, peaceful retreat, playful childhood memories or an adventurous outing. Beaches are living, constantly changing ecosystems, but a simple shift in wind direction can transform tranquil lapping waves into a roaring intense surf. When the waves get large and a surf forms, strong rip currents will forms as well, creating dangerous conditions for swimmers.
As waves crash onto the shore, their natural motion is to retreat back to the ocean. Waves travel in circular motions. However, sometimes natural man-made and natural barriers, like piers and sandbars, block the seaward motion of the waves. The trapped water forms a current that flows along the shore, searching for a break in the barrier.
When this break occurs, the constricted current flows quickly seaward. This fast moving seaward current is called a rip current. People caught in rip currents often panic and try to swim against the current. With an average speed of 1-2 meters/second, these attempts can result with life threatening and sometimes fatal consequences.
I didnt know if I was actually going to make it back to the beach. It was a danger day, but it was a sunny danger day and that is a very bad combination. This is the first time Ive been back. Its not so much that I am afraid of the beach, I just didnt want to walk over the stairs and see where we were and have it all come back.
There were a lot of waves on the beach that day, but wed swam in large waves before so we thought it was no big deal. We were advising people not to go in the supervised area. We tried to swim back in and we realized that we were not getting anywhere. It became pretty clear that they were in trouble.
I knew about rip currents, but I thought I was a strong swimmer and I thought that I could get out of it. Its like swimming on a treadmill, you dont get anywhere, in fact you move backwards. I turned around to my boyfriend and I asked him if he could get out and he couldnt either. Hes two years in the Navy and he's a really strong swimmer and he's a really big guy and I figured that he could fight through anything.
Initially I was excited at the chance for a rescue, that's always kind of an exciting time, but once we got into the water and saw how dangerous is was it was more..I got a little anxious wondering if we could actually get these people in. There was actually a point out there where we thought maybe we weren't sure we could really do this. The waves were getting really bad and we were starting to lose a lot of energy. I kept going under the water and the waves kept coming over my head.
They were actually surprised at the strength of the water I think. A lot of panic coming from these people... They were convinced that they were going to die. So four of us took a rescue can and the other guard took the rescue board which was really helpful in this rescue.
When you are actually in it you dont think of anything but I've gotta get right back to that beach. They try to swim straight in, because the only thing in their mind is to get into shore. Where as if you swim out of it, to the side, along the beach, and then in, you are wasting a lot less energy and you are out of that current that is pulling you out. Look for an area where maybe you see crashing waves and you know that there isnt a current ripping out and swim in that direction.
I was relieved and amazed that I was even back on land and in retrospect I should have swam sideways and tried to get out that way. Talk to your surfguards, they should be able to tell you where rip currents are located, the safest areas that you can swim in and give them tips on what to do if something happens. ...Because I have this experience now, I probably wont freak out as much. Ill be able to use my logic and remember what I know, and how to swim and if nothing else to wait it out.
Carolyns story had a happy ending, but for over 100 people every year in North America this is not the case. Increasing public awareness of rip currents can prevent events like this from occurring at all. One of the myths about rip currents is that they are the same as undertows or rip tides. A rip current will not pull you underwater; they are narrow, strong currents that pull you away from shore.
Not all rip currents look the same. Although some are well formed, most are unstable and difficult the average person to see. Some cues you can look for are the color of the water and variations in wave patterns. Since rip currents create a channel of water, the water may appear darker in color.
It may also be demarked with churned up sand, foam or debris moving in a seaward direction. The channels are generally narrow, less than 10 meters wide. Wave shapes or breaking points are different in rip currents. Look for variations in wave patterns, such as choppy water, leading to a plume beyond the breakers or sandbars.
Be careful of areas of calm water amidst the surf. The unassuming calm water may lure people to swim there but the calm water likely represents deep rip currents and can be very dangerous. Since visual cues are not easily identifiable, most people realize they are in a rip current when they feel themselves being pulled along the shore or in a seaward direction. Rip currents will often have long-shore or lateral currents that lead into the seaward rip current.
When you are knee deep in the water, ask yourself, do you feel the water pulling at you? This can indicate that a rip current is nearby. By getting to know your beaches, you can gain knowledge about where danger spots might develop. Pay particular attention around man-made structures like piers and breakwaters where rip currents are prevalent. The ocean floor and most notably, sandbars, contribute to rip currents as well.
Waves get trapped between the beach and the sandbars. Watch the sandbars as they form; it is in the breaks between sandbars where that trapped water will escape and a rip current is born. Be aware that rip currents can change from day to day and significantly alter after storm events. If you find yourself caught in a rip current remember these key points to breaking the grip of the rip.
Don't panic and don't fight it. A rip current will not take you miles off shore. The strength of the current will lessen the further away from the shore you are. Some very strong rip currents may extend 300 meters off shore, but most will end just past the breaking waves.
A natural reaction when being pulled away from the shoreline is to swim towards it, but this is where people get into trouble. Averaging in speed between 1-2 meters/second, any swimmer, regardless of their strength, will tire easily in trying to swim against the rip. Fatalities result when the tired swimmer no longer has the strength to swim. Dont swim against the current, stay calm and conserve your energy.
Swim out of the current in a direction following the shoreline, when you are out of the current, then swim back to shore. Remember, rip currents are narrow. Swimming parallel to shore takes a fraction of the energy needed to swim against a rip. If you cant swim out of the rip, just tread water.
When the current lessens, swim diagonally back to shore. If you can, try to get attention from shore. If you witness someone in distress in the water, do not enter the water. Get help from a surfguard or call 9-1-1.
Throw them a life-ring or a floatable object to grasp a hold of. Keep in visual contact with them. Remember, good intentioned bystanders often drown themselves trying to perform rescue. Keep safe this summer by learning the warning signs of rip currents and listening to warnings from surfguards.
Before heading out to beach, learn about daily weather & surf conditions Never swim alone. Use supervised swimming areas & learn more about rip currents from your local surfguards. Remember, never swim against a rip, break the grip of the rip by swimming parallel to shore and then swim back to the beach. And...
When in doubt, dont go out! Every year we continue to have a couple of rescue days, which just goes to show that there is a lot of education that needs to be done. Respect the water and don't ever swim alone. Share this knowledge with your family & friends, and help us break the grip of the rip once and for all..Putri LaksmiDecember 10, 2017AdminBandung Indonesia
The allure of sun, sand and the ocean are synonymous with summer. The beach can provide us with a calm, peaceful retreat, playful childhood memories or an adventurous outing. Beaches are living, constantly changing ecosystems, but a simple shift in wind direction can transform tranquil lapping waves into a roaring intense surf. When the waves get large and a surf forms, strong rip currents will forms as well, creating dangerous conditions for swimmers.
As waves crash onto the shore, their natural motion is to retreat back to the ocean. Waves travel in circular motions. However, sometimes natural man-made and natural barriers, like piers and sandbars, block the seaward motion of the waves. The trapped water forms a current that flows along the shore, searching for a break in the barrier.
When this break occurs, the constricted current flows quickly seaward. This fast moving seaward current is called a rip current. People caught in rip currents often panic and try to swim against the current. With an average speed of 1-2 meters/second, these attempts can result with life threatening and sometimes fatal consequences.
I didnt know if I was actually going to make it back to the beach. It was a danger day, but it was a sunny danger day and that is a very bad combination. This is the first time Ive been back. Its not so much that I am afraid of the beach, I just didnt want to walk over the stairs and see where we were and have it all come back.
There were a lot of waves on the beach that day, but wed swam in large waves before so we thought it was no big deal. We were advising people not to go in the supervised area. We tried to swim back in and we realized that we were not getting anywhere. It became pretty clear that they were in trouble.
I knew about rip currents, but I thought I was a strong swimmer and I thought that I could get out of it. Its like swimming on a treadmill, you dont get anywhere, in fact you move backwards. I turned around to my boyfriend and I asked him if he could get out and he couldnt either. Hes two years in the Navy and he's a really strong swimmer and he's a really big guy and I figured that he could fight through anything.
Initially I was excited at the chance for a rescue, that's always kind of an exciting time, but once we got into the water and saw how dangerous is was it was more..I got a little anxious wondering if we could actually get these people in. There was actually a point out there where we thought maybe we weren't sure we could really do this. The waves were getting really bad and we were starting to lose a lot of energy. I kept going under the water and the waves kept coming over my head.
They were actually surprised at the strength of the water I think. A lot of panic coming from these people... They were convinced that they were going to die. So four of us took a rescue can and the other guard took the rescue board which was really helpful in this rescue.
When you are actually in it you dont think of anything but I've gotta get right back to that beach. They try to swim straight in, because the only thing in their mind is to get into shore. Where as if you swim out of it, to the side, along the beach, and then in, you are wasting a lot less energy and you are out of that current that is pulling you out. Look for an area where maybe you see crashing waves and you know that there isnt a current ripping out and swim in that direction.
I was relieved and amazed that I was even back on land and in retrospect I should have swam sideways and tried to get out that way. Talk to your surfguards, they should be able to tell you where rip currents are located, the safest areas that you can swim in and give them tips on what to do if something happens. ...Because I have this experience now, I probably wont freak out as much. Ill be able to use my logic and remember what I know, and how to swim and if nothing else to wait it out.
Carolyns story had a happy ending, but for over 100 people every year in North America this is not the case. Increasing public awareness of rip currents can prevent events like this from occurring at all. One of the myths about rip currents is that they are the same as undertows or rip tides. A rip current will not pull you underwater; they are narrow, strong currents that pull you away from shore.
Not all rip currents look the same. Although some are well formed, most are unstable and difficult the average person to see. Some cues you can look for are the color of the water and variations in wave patterns. Since rip currents create a channel of water, the water may appear darker in color.
It may also be demarked with churned up sand, foam or debris moving in a seaward direction. The channels are generally narrow, less than 10 meters wide. Wave shapes or breaking points are different in rip currents. Look for variations in wave patterns, such as choppy water, leading to a plume beyond the breakers or sandbars.
Be careful of areas of calm water amidst the surf. The unassuming calm water may lure people to swim there but the calm water likely represents deep rip currents and can be very dangerous. Since visual cues are not easily identifiable, most people realize they are in a rip current when they feel themselves being pulled along the shore or in a seaward direction. Rip currents will often have long-shore or lateral currents that lead into the seaward rip current.
When you are knee deep in the water, ask yourself, do you feel the water pulling at you? This can indicate that a rip current is nearby. By getting to know your beaches, you can gain knowledge about where danger spots might develop. Pay particular attention around man-made structures like piers and breakwaters where rip currents are prevalent. The ocean floor and most notably, sandbars, contribute to rip currents as well.
Waves get trapped between the beach and the sandbars. Watch the sandbars as they form; it is in the breaks between sandbars where that trapped water will escape and a rip current is born. Be aware that rip currents can change from day to day and significantly alter after storm events. If you find yourself caught in a rip current remember these key points to breaking the grip of the rip.
Don't panic and don't fight it. A rip current will not take you miles off shore. The strength of the current will lessen the further away from the shore you are. Some very strong rip currents may extend 300 meters off shore, but most will end just past the breaking waves.
A natural reaction when being pulled away from the shoreline is to swim towards it, but this is where people get into trouble. Averaging in speed between 1-2 meters/second, any swimmer, regardless of their strength, will tire easily in trying to swim against the rip. Fatalities result when the tired swimmer no longer has the strength to swim. Dont swim against the current, stay calm and conserve your energy.
Swim out of the current in a direction following the shoreline, when you are out of the current, then swim back to shore. Remember, rip currents are narrow. Swimming parallel to shore takes a fraction of the energy needed to swim against a rip. If you cant swim out of the rip, just tread water.
When the current lessens, swim diagonally back to shore. If you can, try to get attention from shore. If you witness someone in distress in the water, do not enter the water. Get help from a surfguard or call 9-1-1.
Throw them a life-ring or a floatable object to grasp a hold of. Keep in visual contact with them. Remember, good intentioned bystanders often drown themselves trying to perform rescue. Keep safe this summer by learning the warning signs of rip currents and listening to warnings from surfguards.
Before heading out to beach, learn about daily weather & surf conditions Never swim alone. Use supervised swimming areas & learn more about rip currents from your local surfguards. Remember, never swim against a rip, break the grip of the rip by swimming parallel to shore and then swim back to the beach. And...
When in doubt, dont go out! Every year we continue to have a couple of rescue days, which just goes to show that there is a lot of education that needs to be done. Respect the water and don't ever swim alone. Share this knowledge with your family & friends, and help us break the grip of the rip once and for all..
You might have heard them referred to as undertow
or rip tides, but these ocean phenomena are actually rip currents. Rip currents are narrow currents in the surf
zone that move quickly away from shore. A typical rip current ranges from 50-100 feet
wide, and can extend 100 yards or more offshore. It can reach speeds of over 5 miles per hour
- thats faster than an Olympic swimmer! That makes them dangerous and potentially
deadly, and scientists want to learn more about them so we can better forecast when
and where they will form - and keep beachgoers safe.
Heres what we know: Waves dont have to be huge for a rip current
to form - two or three feet are all it takes. And the weather doesnt have to be bad for
a rip current to emerge. They often occur in the nice days after a storm. Theyre usually strongest near low tide,
but can form at any time.
Rip currents often form where sand bars are
near the shore. They occur at breaks or channels in the bar. Theyre often difficult to see, but you
can spot them in areas where waves arent breaking, or where theres foam, seaweed,
or discolored water being pulled offshore. Its easier to see a rip current from higher
up - such as from the beach access over dunes or a lifeguards tower.
Rip currents are a hazard for beachgoers,
but by knowing the dangers and what to look for, you can avoid being caught in the grip
of the rip..Putri LaksmiDecember 10, 2017AdminBandung Indonesia
You might have heard them referred to as undertow
or rip tides, but these ocean phenomena are actually rip currents. Rip currents are narrow currents in the surf
zone that move quickly away from shore. A typical rip current ranges from 50-100 feet
wide, and can extend 100 yards or more offshore. It can reach speeds of over 5 miles per hour
- thats faster than an Olympic swimmer! That makes them dangerous and potentially
deadly, and scientists want to learn more about them so we can better forecast when
and where they will form - and keep beachgoers safe.
Heres what we know: Waves dont have to be huge for a rip current
to form - two or three feet are all it takes. And the weather doesnt have to be bad for
a rip current to emerge. They often occur in the nice days after a storm. Theyre usually strongest near low tide,
but can form at any time.
Rip currents often form where sand bars are
near the shore. They occur at breaks or channels in the bar. Theyre often difficult to see, but you
can spot them in areas where waves arent breaking, or where theres foam, seaweed,
or discolored water being pulled offshore. Its easier to see a rip current from higher
up - such as from the beach access over dunes or a lifeguards tower.
Rip currents are a hazard for beachgoers,
but by knowing the dangers and what to look for, you can avoid being caught in the grip
of the rip..
Okay in today's video I am going to go
over how to calculate and determine the resistance the current and the voltage
for simple parallel circuits. Okay this is the parallel circuit that we're going
to use is the most common way a parallel circuit is drawn but there is more than
one way to draw them the important thing to notice here is that the voltage
source, our battery, and all of the resistors are parallel to each other and
they actually look like they're each parallel to each other and that's the
biggest hint that you have parallel components in a circuit when they look
like they're parallel and they're usually drawn correctly then it's
probably a parallel circuit okay. Now these are the five things we're going to
do first we're going to get the total voltage gain in the circuit. Then we're
going to get the equivalent resistance or the total resistance as i'd like to
call it in the circuit.
Then the third thing is we're going to get the total
current to the circui. Now these are the things I like to call kind of a big
three. We got to get these three things these totals taken care of
then we can figure out what the voltage drop is across each of the resistors and
then, we can figure out what the current is through each of the three resistors.
Now this circuit has three resistors all these rules apply whether you have two
resistors three resistors four resistors five it does not matter if you had only
one resistor it would actually be a series circuit but if you have more than
one resistor and all these rules that we're going to talk about apply and
we're going to start with the total voltage in the circuit. This is the
voltage gain this is the battery this is the thing that causes the electrons to
gain energy or to get potential electric potential energy there's only one of
them so it's pretty straightforward.
The total voltage gain in the circuit is 20
volts and I like to put down here total because I know that's my total
voltage gain. Okay now we're going to do the equivalent resistance and this is
the tricky part. You remember in series circuits we just added them up this
would be seven fifteen plus twelve you cannot do that you know a parallel
circuit I know you want to because that's the easy way out
but you have to use this scary-looking equation. Now it's not that complicated
but yes to figure out the equivalent resistance you must use this equation
and this equation is simply not just adding them up ok so let's go through
it's 1 over RT which is the total resistance equals 1 over R1 plus 1 over
R2 plus one over R3 so we're simply just going to first plug the numbers in now
it's still just 1 over RT equals 1 over 7 ohms plus 1 over 15 plus 1 over 12
ohms now pick up your calculator and you can just punch these right into your
calculator like this ok it's just simply 1 divided by 7 plus 1 divided by 15 plus
1 divided by 12 and that will give you what 1 over RT equals 1 over R T not
R T this is not the equivalent resistance this is 1 over RT is equal
to 0.293 Now in order to get RT I'm going to take the reciprocal of
this side and the reciprocal of this side if I take the reciprocal of this
side I just get RT if I take the reciprocal of this side I get 1 over 0.293 So in order to figure out what R T is I have to do on my
calculator 1 divided by 0.293 If I do 1 divided by 0.293
Then I will get that the total resistance the equivalent resistance of
that circuit is 3.41 Ohms.
Okay so it's a little bit of math
not that complicated practice figure it out and you'll get the steps down. Now
let's get the total current once again we're going to use Ohm's law and in
order to use Ohm's law we're going to use the current so we want to solve for
I hi stands for the current this is the voltage this is the resistance we're
going to divide each side by R and we're going to get that the total current I
put down I tea because it's the total which is
different than the current through each branch I want to make sure I keep those
things separate from each other. The total current is simply the total
voltage divided by the total resistance. Okay if I use the total voltage and the
total resistance I'll get the total current.
Okay so let's
go through IT equals the total voltage is 20 we determined the total current
excuse me the total resistance is 3.41 And therefore the total
current is 5.87 Amps now we have the total voltage the total resistance
and the total current and those are the first big 3 things we needed to figure
out for that circuit. Ok now we can get the voltage drop the voltage drop across
each resistor. Now we need to think about parallel circuits what is the voltage
rule the rule concerning the voltage drops well we talked earlier that the
rule is that the voltage drop across each resistor one two and three is equal
to the voltage gain from the battery all right so they're all equal to each other.
Now let me just point out I'm trying to show you why let's look at this resistor
between this resistor and the battery there really are no elements in the
circuit that are going to use any power or any energy. Yes this one is kind of
between it but if you follow this resistor back to the battery on both
sides back to the battery ok just take your fingers and put it on the diagram
there's nothing between that resistor and the path back to the battery.
So
there's nothing that's going to use any of the energy that would be delivered to
that resistor ok there was another resistor here or here or down below then
there would be something that would be using some of that energy but there's
nothing between any of these resistors this one goes right back this one goes
right back so they all get the full power from the battery and that's why
that works out like that. So if we want to know what the voltage drop is the
amount of energy used by resistor number one is just equal to the
voltage from the battery the total voltage 20 volts okay same thing for
number two and same thing for number three but each equal to the total
voltage or the voltage from the battery. Okay now that seems a little hard but
there if you think about it they're really all just connected right back to
the battery okay now we're going to go and do the fifth thing which is the
current through each resistor now we have to think about parallel circuits
what's the rule for the current the current rule is that the current through
each branch, through each resistor. Branch 1, branch 2, branch 3.
The current
through each branch is going to equal the total now we set earlier the total
is 5.87 Amps that's the current that comes out of this part
of the circuit comes out of the battery. Well you have to kind of think about it
a little bit conceptually right here at this point we call this a node and
there's a split some of the current is going to go here the remainder of the
current is going to go here. There's another node right here some of the
current is going to go this way and some of the current is going to continue
through and they will actually all come back and add up. So the total current is
the same here and here but through the branches it's going to be different now
the branches there's three branches each gets some of the current so when we add
them up you get the total.
Now in order to calculate them we're going to have to
use Ohm's law again and we're going to have to use those for the current now we
want to find the current to a number one so we have to get the voltage through
number one and divide that by the resistance of number one. This resistance,
not this resistant that's why I like to write down I1 V1 R1. Okay if you want
I1 you have to use V1 and R1 V1 is 20 volts same as the total which we got
in the previous slide and this is R 1 is 7 and that's 2.86 Amps of
current through that branch now we have I2 we're going to take V2
which is still 20 divided by R2 which is now 15 which is 15 and you get that the
current through the second branch is 1.34 You'll notice the resistance is
higher, this is 7 this is 15 so this is going to be less okay and this is about
twice as high so this is twice as less or half as much. Okay, now the third one,
now of course this should say I3 but we have V3 and R3.
V3 is 20 all the
voltages with drops are equal to the total this is 12 the resistance of the
third, 12 ohms and you get 1.67 Amps, alright so there we've done
all three currents and let's look back at our rule the current will set these
three currents should add up to the total well let's see two point eight six
plus one point three four plus one point six seven those equal five point eight
seven so if they all add up then we know we have two pretty good feeling we did
that correctly all right. So once again we get the voltage the resistance the
current totals, then we got the voltage across each resistor, then we use the
current rule to get the current through each resistor along with Ohm's law. Okay
so I know that's five steps it's kind of a lot the rules, the equations, write them
all down follow the steps, plug the values in get the answers with the
correct units. Think about your thinking to see if you get everything in the
right order everything makes sense and I.
Think you can do those problems no
problem. Ok thank you for watching and if you enjoyed that video or found it
helpful please leave me a thumbs up or give me a
comment in the comment section below thank you very much.Putri LaksmiDecember 10, 2017AdminBandung Indonesia
Okay in today's video I am going to go
over how to calculate and determine the resistance the current and the voltage
for simple parallel circuits. Okay this is the parallel circuit that we're going
to use is the most common way a parallel circuit is drawn but there is more than
one way to draw them the important thing to notice here is that the voltage
source, our battery, and all of the resistors are parallel to each other and
they actually look like they're each parallel to each other and that's the
biggest hint that you have parallel components in a circuit when they look
like they're parallel and they're usually drawn correctly then it's
probably a parallel circuit okay. Now these are the five things we're going to
do first we're going to get the total voltage gain in the circuit. Then we're
going to get the equivalent resistance or the total resistance as i'd like to
call it in the circuit.
Then the third thing is we're going to get the total
current to the circui. Now these are the things I like to call kind of a big
three. We got to get these three things these totals taken care of
then we can figure out what the voltage drop is across each of the resistors and
then, we can figure out what the current is through each of the three resistors.
Now this circuit has three resistors all these rules apply whether you have two
resistors three resistors four resistors five it does not matter if you had only
one resistor it would actually be a series circuit but if you have more than
one resistor and all these rules that we're going to talk about apply and
we're going to start with the total voltage in the circuit. This is the
voltage gain this is the battery this is the thing that causes the electrons to
gain energy or to get potential electric potential energy there's only one of
them so it's pretty straightforward.
The total voltage gain in the circuit is 20
volts and I like to put down here total because I know that's my total
voltage gain. Okay now we're going to do the equivalent resistance and this is
the tricky part. You remember in series circuits we just added them up this
would be seven fifteen plus twelve you cannot do that you know a parallel
circuit I know you want to because that's the easy way out
but you have to use this scary-looking equation. Now it's not that complicated
but yes to figure out the equivalent resistance you must use this equation
and this equation is simply not just adding them up ok so let's go through
it's 1 over RT which is the total resistance equals 1 over R1 plus 1 over
R2 plus one over R3 so we're simply just going to first plug the numbers in now
it's still just 1 over RT equals 1 over 7 ohms plus 1 over 15 plus 1 over 12
ohms now pick up your calculator and you can just punch these right into your
calculator like this ok it's just simply 1 divided by 7 plus 1 divided by 15 plus
1 divided by 12 and that will give you what 1 over RT equals 1 over R T not
R T this is not the equivalent resistance this is 1 over RT is equal
to 0.293 Now in order to get RT I'm going to take the reciprocal of
this side and the reciprocal of this side if I take the reciprocal of this
side I just get RT if I take the reciprocal of this side I get 1 over 0.293 So in order to figure out what R T is I have to do on my
calculator 1 divided by 0.293 If I do 1 divided by 0.293
Then I will get that the total resistance the equivalent resistance of
that circuit is 3.41 Ohms.
Okay so it's a little bit of math
not that complicated practice figure it out and you'll get the steps down. Now
let's get the total current once again we're going to use Ohm's law and in
order to use Ohm's law we're going to use the current so we want to solve for
I hi stands for the current this is the voltage this is the resistance we're
going to divide each side by R and we're going to get that the total current I
put down I tea because it's the total which is
different than the current through each branch I want to make sure I keep those
things separate from each other. The total current is simply the total
voltage divided by the total resistance. Okay if I use the total voltage and the
total resistance I'll get the total current.
Okay so let's
go through IT equals the total voltage is 20 we determined the total current
excuse me the total resistance is 3.41 And therefore the total
current is 5.87 Amps now we have the total voltage the total resistance
and the total current and those are the first big 3 things we needed to figure
out for that circuit. Ok now we can get the voltage drop the voltage drop across
each resistor. Now we need to think about parallel circuits what is the voltage
rule the rule concerning the voltage drops well we talked earlier that the
rule is that the voltage drop across each resistor one two and three is equal
to the voltage gain from the battery all right so they're all equal to each other.
Now let me just point out I'm trying to show you why let's look at this resistor
between this resistor and the battery there really are no elements in the
circuit that are going to use any power or any energy. Yes this one is kind of
between it but if you follow this resistor back to the battery on both
sides back to the battery ok just take your fingers and put it on the diagram
there's nothing between that resistor and the path back to the battery.
So
there's nothing that's going to use any of the energy that would be delivered to
that resistor ok there was another resistor here or here or down below then
there would be something that would be using some of that energy but there's
nothing between any of these resistors this one goes right back this one goes
right back so they all get the full power from the battery and that's why
that works out like that. So if we want to know what the voltage drop is the
amount of energy used by resistor number one is just equal to the
voltage from the battery the total voltage 20 volts okay same thing for
number two and same thing for number three but each equal to the total
voltage or the voltage from the battery. Okay now that seems a little hard but
there if you think about it they're really all just connected right back to
the battery okay now we're going to go and do the fifth thing which is the
current through each resistor now we have to think about parallel circuits
what's the rule for the current the current rule is that the current through
each branch, through each resistor. Branch 1, branch 2, branch 3.
The current
through each branch is going to equal the total now we set earlier the total
is 5.87 Amps that's the current that comes out of this part
of the circuit comes out of the battery. Well you have to kind of think about it
a little bit conceptually right here at this point we call this a node and
there's a split some of the current is going to go here the remainder of the
current is going to go here. There's another node right here some of the
current is going to go this way and some of the current is going to continue
through and they will actually all come back and add up. So the total current is
the same here and here but through the branches it's going to be different now
the branches there's three branches each gets some of the current so when we add
them up you get the total.
Now in order to calculate them we're going to have to
use Ohm's law again and we're going to have to use those for the current now we
want to find the current to a number one so we have to get the voltage through
number one and divide that by the resistance of number one. This resistance,
not this resistant that's why I like to write down I1 V1 R1. Okay if you want
I1 you have to use V1 and R1 V1 is 20 volts same as the total which we got
in the previous slide and this is R 1 is 7 and that's 2.86 Amps of
current through that branch now we have I2 we're going to take V2
which is still 20 divided by R2 which is now 15 which is 15 and you get that the
current through the second branch is 1.34 You'll notice the resistance is
higher, this is 7 this is 15 so this is going to be less okay and this is about
twice as high so this is twice as less or half as much. Okay, now the third one,
now of course this should say I3 but we have V3 and R3.
V3 is 20 all the
voltages with drops are equal to the total this is 12 the resistance of the
third, 12 ohms and you get 1.67 Amps, alright so there we've done
all three currents and let's look back at our rule the current will set these
three currents should add up to the total well let's see two point eight six
plus one point three four plus one point six seven those equal five point eight
seven so if they all add up then we know we have two pretty good feeling we did
that correctly all right. So once again we get the voltage the resistance the
current totals, then we got the voltage across each resistor, then we use the
current rule to get the current through each resistor along with Ohm's law. Okay
so I know that's five steps it's kind of a lot the rules, the equations, write them
all down follow the steps, plug the values in get the answers with the
correct units. Think about your thinking to see if you get everything in the
right order everything makes sense and I.
Think you can do those problems no
problem. Ok thank you for watching and if you enjoyed that video or found it
helpful please leave me a thumbs up or give me a
comment in the comment section below thank you very much.
Let's explore the repercussions
of this equation some more. So what was the equation? It was that the force of a
magnetic field on a moving charged particle is equal to the
charge-- that's not what I. Wanted to do-- is equal to the
charge of the particle-- and that's just a scalar quantity--
times the velocity-- the cross product
of the velocity of the particle-- with the
magnetic field. Now, isn't the velocity vector
just the same thing as the distance vector divided
by time? So the velocity vector is equal
to-- let's call the distance that the electron
travels, l.
Distance divided by time. So we could rewrite that, that
the force vector is equal to the charge times-- and I'm doing
this on purpose-- 1 over time, right? Times the distance vector
taken-- you take the cross product with the
magnetic field. All I did is I rewrote velocity
as per time times distance, or distance
per time. And this is a scalar quantity,
at least for our purposes, time only has a magnitude.
Maybe we could call
it change in time. But it doesn't have
a direction. We're not going at
an angle in time. So we could take the scalar
quantity out.
It doesn't affect this
vector cross product. So what we get left with is,
force is equal to charge per time times-- and this is just a
regular times, because this is just a number, it's not a
vector-- times the cross product of the distance vector
and the magnetic field. And what is charge per time? Coulombs per second? Well, that's just current. So we get that force is equal to
current times the distance that the current is flowing
along, taken-- and you take the cross product of that
with the magnetic field.
And sometimes this is written as
a capital L because it's a vector and all that, but we
started with a lower case l, so we'll stay with
the lower case l. So let's see if we can apply
this formula, which is really the same thing as this. We just took the division by
time and took it out of velocity so we get distance. And we took it and we divided
the coulombs, or we took the charge divided by that.
So we took charge divided by
time, or charge per unit of time, you get current. So this is really just another
way of writing this. It's not even a new formula. You could almost prove
it to yourself if you ever forget it.
But let's see if we can use this
to figure out the effect that a magnetic field has on
a current carrying wire. So let me-- actually, I probably
want to put this up at the top, just so that I have
space to draw a current carrying wire. So let me rewrite it in green. So you're familiar with the
formula in all colors.
So now our new derivation is
that the force of a magnetic field on a current carrying wire
is equal to the current in the wire-- and that's just a
scalar quantity, although it could be positive or negative
depending on the direction. Well, current is always a
positive number, but if this current is going in the opposite
direction as our distance vector, then it
might be negative. But I wouldn't worry
about that for now. Let's just assume this is a
current in the direction of the distance vector.
So it's a scalar quantity
current times our distance vector l, or maybe the length
of the conductor. You take the cross product
of l with the magnetic field vector. So let's see if we
can apply that. Let's say that we have a wire.
Actually, let's do the magnetic
field first. I've been doing a lot of magnetic
fields that pop out of the screen. Let's do a magnetic field that
goes into the screen. And those are even
easier to draw.
They're just x's. Now, why is it an x? Because you're looking at the
rear end of an arrow. That's why it's an x. And that's why a circle with a
dot means a field or a vector coming out of the window.
Because if an arrow was shot at
you, all you would see is the tip of the arrow
with maybe a little circle around it. But anyway, this shows us a
vector going into the screen. So this is our magnetic field. That is B.
I don't know, let's
assign some value. Let's say that the magnitude
of B is equal to 1 tesla. And let's say I have a
wire going through that magnetic field. Let's say the wire is going
along or it's in the plane of your computer monitor.
Let me just draw a wire going
through the magnetic field. And my question to you-- let
me tell you a little bit of information about this wire. Let's say the wire is
carrying a current. So I is going in
that direction.
And it is carrying a current
of-- I'm just making up numbers-- 5 amperes, or
5 coulombs per second. My question to you is, what is
the net force of this magnetic field on a section
of this wire? And let's make this section of
the wire, I don't know, let's say it's a 2 meter
section of wire. So obviously the more wire you
have, the more charged moving particles you'll have. So the
larger a section you have, the more of a force you'll have on
that longer piece of wire.
So we have to pick our length. So we want to know, what is
the force of the magnetic field on this section of wire? From here to here. So let's just go to
this formula. The force is equal
to the current.
So that's 5 amperes. And remember, just from what we
learned about electricity, the current is the direction
that notional positive charges would travel in, and
suits us fine. Because when we did the first
equation, we cared about the direction a positive
charge would go in. And if it was an electron or a
negative charge, we would put a negative sign there.
So that works fine. But if you ever have to
visualize things as they maybe are in reality, but when you
talk about electrons it's hard to say that they really are
reality, because they're almost more an idea
than an object. But it's always good to remember
that when the current is flowing in this direction,
that would be true. Because if they were positive
charges moving, but we know it's a negative charge moving
in the opposite direction.
Or you can think of it
as, maybe, holes. Well, I don't want
to get into that. But anyway, the current-- you
could visualize it if you like as positive charges going
in this direction. So the current is going
this direction.
So you could view this
distance vector that we care about. Its magnitude is 2 meters. Because that's the length
of wire in question. And its direction is the
direction of the current.
So let me-- this is l. Sometimes I get a little carried
away on tangents. So that is l. It's 2 meters in
that direction.
I is 5 amperes. And we already figured
out that the magnetic field is 1 tesla. So what's this going
to be equal to? So the force is going to be
equal to-- we're using all SI. Units, so we don't have to
convert anything-- 5 amperes times 2 meters in
that direction.
I won't specify right now,
let's just say that's a magnitude of l. Actually, let me write it. Well, 2 meters times the
magnetic field, 1 tesla. And so when you take a cross
product of something, this is just a reminder.
L cross B. That's equal to the magnitude of
l times the magnitude of B. Times the sine of the angle
between them times some unit directional vector that
we figure out with the right hand rule. So we already did
the magnitude of the distance vector.
That was 2 meters. We did the magnitude of
the magnetic field. And what's the sine of the
angle between them? Well, if the magnetic field is
going into the screen, if it's going straight into the screen,
you could imagine a bunch of arrows shooting
into the screen. Those are the vectors.
While our distance vector, or
this l is in the screen, they actually are perpendicular,
in 3 dimensions. So this angle is 90 degrees. So this actually
just becomes 1. So in terms of the magnitude,
we're done.
The l cross B magnitude
is 2 times 1 tesla. And then we multiply that
times the current. And then we actually have the
magnitude of the force. The magnitude of this force is
going to be equal to 5 amperes times 2 meters times 1 tesla.
Which is equal to 10 newtons. And then the only question left
is, what is the direction of the force that the magnetic
field is exerting? And this is where we break
out the right hand rule. And it's no different. You could just imagine one of
the positive particles moving in that direction, and just
use the right hand rule.
So let's take our hand out. And if we-- let me
draw a hand. A right hand. So this is my right hand.
If I have my thumb sticking
out like that. So the l is going to
be my index finger. The first thing in the
cross product. And then the B is the
magnetic field.
That's going into the screen. So you can't see it. All you can take my word for it
is that my middle finger is pointed downwards into the
screen and then my other fingers are just doing
something else. And there you have it.
Your thumb is actually the
direction of the force. Your index finger is the
direction of-- we'll say l for these purposes. And then the magnetic field is
going into it, so you can't see my middle finger but it's
pointing downwards. I could draw a little x there,
to show it's going downwards.
And then the force is what
my thumb is doing. So the force on this wire, or
at least on that section of wire, is going to be
perpendicular to the direction of the current. And that direction is going
to be a 10 newton force. Anyway, I've run out of time..Putri LaksmiDecember 10, 2017AdminBandung Indonesia
Let's explore the repercussions
of this equation some more. So what was the equation? It was that the force of a
magnetic field on a moving charged particle is equal to the
charge-- that's not what I. Wanted to do-- is equal to the
charge of the particle-- and that's just a scalar quantity--
times the velocity-- the cross product
of the velocity of the particle-- with the
magnetic field. Now, isn't the velocity vector
just the same thing as the distance vector divided
by time? So the velocity vector is equal
to-- let's call the distance that the electron
travels, l.
Distance divided by time. So we could rewrite that, that
the force vector is equal to the charge times-- and I'm doing
this on purpose-- 1 over time, right? Times the distance vector
taken-- you take the cross product with the
magnetic field. All I did is I rewrote velocity
as per time times distance, or distance
per time. And this is a scalar quantity,
at least for our purposes, time only has a magnitude.
Maybe we could call
it change in time. But it doesn't have
a direction. We're not going at
an angle in time. So we could take the scalar
quantity out.
It doesn't affect this
vector cross product. So what we get left with is,
force is equal to charge per time times-- and this is just a
regular times, because this is just a number, it's not a
vector-- times the cross product of the distance vector
and the magnetic field. And what is charge per time? Coulombs per second? Well, that's just current. So we get that force is equal to
current times the distance that the current is flowing
along, taken-- and you take the cross product of that
with the magnetic field.
And sometimes this is written as
a capital L because it's a vector and all that, but we
started with a lower case l, so we'll stay with
the lower case l. So let's see if we can apply
this formula, which is really the same thing as this. We just took the division by
time and took it out of velocity so we get distance. And we took it and we divided
the coulombs, or we took the charge divided by that.
So we took charge divided by
time, or charge per unit of time, you get current. So this is really just another
way of writing this. It's not even a new formula. You could almost prove
it to yourself if you ever forget it.
But let's see if we can use this
to figure out the effect that a magnetic field has on
a current carrying wire. So let me-- actually, I probably
want to put this up at the top, just so that I have
space to draw a current carrying wire. So let me rewrite it in green. So you're familiar with the
formula in all colors.
So now our new derivation is
that the force of a magnetic field on a current carrying wire
is equal to the current in the wire-- and that's just a
scalar quantity, although it could be positive or negative
depending on the direction. Well, current is always a
positive number, but if this current is going in the opposite
direction as our distance vector, then it
might be negative. But I wouldn't worry
about that for now. Let's just assume this is a
current in the direction of the distance vector.
So it's a scalar quantity
current times our distance vector l, or maybe the length
of the conductor. You take the cross product
of l with the magnetic field vector. So let's see if we
can apply that. Let's say that we have a wire.
Actually, let's do the magnetic
field first. I've been doing a lot of magnetic
fields that pop out of the screen. Let's do a magnetic field that
goes into the screen. And those are even
easier to draw.
They're just x's. Now, why is it an x? Because you're looking at the
rear end of an arrow. That's why it's an x. And that's why a circle with a
dot means a field or a vector coming out of the window.
Because if an arrow was shot at
you, all you would see is the tip of the arrow
with maybe a little circle around it. But anyway, this shows us a
vector going into the screen. So this is our magnetic field. That is B.
I don't know, let's
assign some value. Let's say that the magnitude
of B is equal to 1 tesla. And let's say I have a
wire going through that magnetic field. Let's say the wire is going
along or it's in the plane of your computer monitor.
Let me just draw a wire going
through the magnetic field. And my question to you-- let
me tell you a little bit of information about this wire. Let's say the wire is
carrying a current. So I is going in
that direction.
And it is carrying a current
of-- I'm just making up numbers-- 5 amperes, or
5 coulombs per second. My question to you is, what is
the net force of this magnetic field on a section
of this wire? And let's make this section of
the wire, I don't know, let's say it's a 2 meter
section of wire. So obviously the more wire you
have, the more charged moving particles you'll have. So the
larger a section you have, the more of a force you'll have on
that longer piece of wire.
So we have to pick our length. So we want to know, what is
the force of the magnetic field on this section of wire? From here to here. So let's just go to
this formula. The force is equal
to the current.
So that's 5 amperes. And remember, just from what we
learned about electricity, the current is the direction
that notional positive charges would travel in, and
suits us fine. Because when we did the first
equation, we cared about the direction a positive
charge would go in. And if it was an electron or a
negative charge, we would put a negative sign there.
So that works fine. But if you ever have to
visualize things as they maybe are in reality, but when you
talk about electrons it's hard to say that they really are
reality, because they're almost more an idea
than an object. But it's always good to remember
that when the current is flowing in this direction,
that would be true. Because if they were positive
charges moving, but we know it's a negative charge moving
in the opposite direction.
Or you can think of it
as, maybe, holes. Well, I don't want
to get into that. But anyway, the current-- you
could visualize it if you like as positive charges going
in this direction. So the current is going
this direction.
So you could view this
distance vector that we care about. Its magnitude is 2 meters. Because that's the length
of wire in question. And its direction is the
direction of the current.
So let me-- this is l. Sometimes I get a little carried
away on tangents. So that is l. It's 2 meters in
that direction.
I is 5 amperes. And we already figured
out that the magnetic field is 1 tesla. So what's this going
to be equal to? So the force is going to be
equal to-- we're using all SI. Units, so we don't have to
convert anything-- 5 amperes times 2 meters in
that direction.
I won't specify right now,
let's just say that's a magnitude of l. Actually, let me write it. Well, 2 meters times the
magnetic field, 1 tesla. And so when you take a cross
product of something, this is just a reminder.
L cross B. That's equal to the magnitude of
l times the magnitude of B. Times the sine of the angle
between them times some unit directional vector that
we figure out with the right hand rule. So we already did
the magnitude of the distance vector.
That was 2 meters. We did the magnitude of
the magnetic field. And what's the sine of the
angle between them? Well, if the magnetic field is
going into the screen, if it's going straight into the screen,
you could imagine a bunch of arrows shooting
into the screen. Those are the vectors.
While our distance vector, or
this l is in the screen, they actually are perpendicular,
in 3 dimensions. So this angle is 90 degrees. So this actually
just becomes 1. So in terms of the magnitude,
we're done.
The l cross B magnitude
is 2 times 1 tesla. And then we multiply that
times the current. And then we actually have the
magnitude of the force. The magnitude of this force is
going to be equal to 5 amperes times 2 meters times 1 tesla.
Which is equal to 10 newtons. And then the only question left
is, what is the direction of the force that the magnetic
field is exerting? And this is where we break
out the right hand rule. And it's no different. You could just imagine one of
the positive particles moving in that direction, and just
use the right hand rule.
So let's take our hand out. And if we-- let me
draw a hand. A right hand. So this is my right hand.
If I have my thumb sticking
out like that. So the l is going to
be my index finger. The first thing in the
cross product. And then the B is the
magnetic field.
That's going into the screen. So you can't see it. All you can take my word for it
is that my middle finger is pointed downwards into the
screen and then my other fingers are just doing
something else. And there you have it.
Your thumb is actually the
direction of the force. Your index finger is the
direction of-- we'll say l for these purposes. And then the magnetic field is
going into it, so you can't see my middle finger but it's
pointing downwards. I could draw a little x there,
to show it's going downwards.
And then the force is what
my thumb is doing. So the force on this wire, or
at least on that section of wire, is going to be
perpendicular to the direction of the current. And that direction is going
to be a 10 newton force. Anyway, I've run out of time..
When positive charges move in
this direction, then per definition,
we say the current goes in this direction.
When negative charges go in this direction,
we also say the current goes in that direction,
that's just our convention. If I apply a potential
difference over a conductor, then I'm going to create an
electric field in that conductor.
And the electrons -- there are free electrons in a conductor --
they can move, but the ions cannot move,
because they are frozen into the solid, into the crystal.
And so when a current flows in a conductor, it's always the
electrons that are responsible for the current.
The electrons fuel the electric fields, and then the electrons
try to make the electric field zero, but they can't succeed,
because we keep the potential difference over the conductor.
Often, there is a linear relationship between current and
the potential, in which case,
we talk about Ohm's Law. Now, I will try to derive Ohm's
Law in a very crude way,
a poor man's version, and not really one hundred
percent kosher, it requires quantum mechanics,
which is beyond the course -- beyond this course -- but I will
do a job that still gives us some interesting insight into
Ohm's Law. If I start off with a
conductor, for instance, copper, at room temperature,
three hundred degrees Kelvin, the free electrons in copper
have a speed, an average speed of about a
million meters per second.
So this is the average speed of
those free electrons, about a million meters per
second. This in all directions.
It's a chaotic motion. It's a thermal motion,
it's due to the temperature. The time between collisions --
time between the collisions -- and this is a collision of the
free electron with the atoms -- is approximately -- I call it
tau -- is about three times ten to the
minus fourteen seconds.
No surprise,
because the speed is enormously high.
And the number of free electrons in copper per cubic
meter, I call that number N, is about ten to the
twenty-nine. There's about one free electron
for every atom. So we get twen- ten to the
twenty-nine free electrons per cubic meter.
So now imagine that I apply a potential difference piece of
copper -- or any conductor, for that matter -- then the
electrons will experience a force which is the charge of the
electron, that's my little E. Times the electric field that
I'm creating, because I apply a potential
difference.
I realize that the force and
the electric field are in opposite directions for
electrons, but that's a detail, I'm interested
in the magnitudes only. And so now these electrons will
experience an acceleration, which is the force divided by
the mass of the electron, and so they will pick up,
eh, speed, between these colli- collisions, which we call the
drift velocity, which is A times tau,
it's just eight oh one. And so A equals F divided by M.
E F is in the A, so we get E times E divided by
the mass of the electrons, times tau.
And that is the the drift velocity.
When the electric field goes up, the drift velocity goes up,
so the electrons move faster in the direction opposite to the
current. If the time between collisions
gets larger, they -- the acceleration lasts longer,
so also, they pick up a larger speed, so that's intuitively
pleasing.
If we take a specific case,
and I take, for instance, copper,
and I apply over the -- over a wire -- let's say the wire has a
length of 10 meters -- I apply a potential difference I call
delta V, but I could have said just V -- I apply there a
potential difference of ten volts, then the electric field
-- inside the conductor, now -- is about one volt per
meter. And so I can calculate,
now, for that specific case, I can calculate what the drift
velocity would be. So the drift velocity of those
free electrons would be the charge of the electron,
which is one point six times ten to the minus nineteen
Coulombs. The E field is one,
so I can forget about that.
Tau is three times ten to the
minus fourteen, as long as I'm room
temperature, and the mass of the electron is about ten to the
minus thirty kilograms. And so, if I didn't slip up,
I found that this is five times ten to the minus three meters
per second, which is half a centimeter per second.
So imagine, due to the thermal motion, these free electrons
move with a million meters per second.
But due to this electric field, they only advance along the
wire slowly, like a snail, with a speed on average of half
a centimeter per second. And that goes very much against
your and my own intuition, but this is the way it is.
I mean, a turtle would go faster than these electrons.
To go along a ten-meter wire would take half hour.
Something that you never thought of.
That it would take a half hour for these electrons to go along
the wire if you apply potential difference of ten volts,
copper ten meters long. Now, I want to massage this
further, and see whether we can somehow
squeeze out Ohm's Law, which is the linear relation
between the potential and the current.
So let me start off with a wire which has a cross-section A,
and it has a length L, and I put a potential
difference over the wire,
plus here, and minus there, potential V,
so I would get a current in this direction,
that's our definition of current, going from plus to
minus.
The electrons,
of course, are moving in this direction, with the drift
velocity. And so the electric field in
here, which is in this direction, that electric field
is approximately V divided by L, potential difference divided by
distance. In one second,
these free electrons will move from left to right over a
distance V D meters. So if I make any cross-section
through this wire, anywhere, I can calculate how
many electrons pass through that cross-section in one second.
In one second, the volume that passes through
here, the volume is V D times A.
But the number of free
electrons per cubic meter is called N, so this is now the
number of free electrons that passes, per second,
through any cross-section. And each electron has a charge
E, and so this is the current that will flow.
The current, of course, is in this
direction, but that's a detail. If I now substitute the drift
velocity, which we have here, I substitute that in there,
but then I find that the current -- I get a E squared,
the charge squared, I get N, I get tau,
I get downstairs, the mass of the electron,
and then I get A times the electric field E.
Because I have here, is electric field E.
When you look at this here, that really depends only on the
properties of by substance, for a given temperature.
And we give that a name. We call this sigma,
which is called conductivity.
Conductivity.
If I calculate, for copper, the conductivity,
at room temperature, that's very easy,
because I've given you what N. Is, on the blackboard there,
ten to the twenty-nine, you know what tau is at room
temperature, three times ten to the minus fourteen,
so for copper, at room temperature,
you will find about ten to the eighth.
You will see more values fro sigma later on during this
course. This is in SI units.
I can massage this a little further, because E is V divided
by L, and so I can write now that the
current is that sigma times A. Times V divided by L.
I can write it down a little bit differently,
I can say V, therefore, equals L divided by
sigma A, times I.
And now, you're staring at
Ohm's Law, whether you like it or not,
because this is what we call the resistance,
capital R. We often write down rho for one
over sigma, and rho is called the resistivity.
So either one will do. So you can also write down --
you can write down V equals I R, and this R, then,
is either L divided by sigma A, or L times rho -- let me make
it a nicer rho -- divided by A. That's the same thing.
The units for resistance R is volts per ampere,
but we call that ohm.
And so the unit for R is ohm.
And so if you want to know what the
unit for rho and sigma is, that follows immediately from
the equations. The unit for rho is then
ohm-meters. So we have derived the
resistance here in terms of the dimensions -- namely,
the length and the cross-section -- but also in
terms of the physics on an atomic scale,
which, all by itself, is interesting.
If you look at the resistance, you see it is proportional with
the length of your wire through
which you drive a current. Think of this as water trying
to go through a pipe.
If you make the pipe longer,
the resistance goes up, so that's very intuitively
pleasing. Notice that you have A
downstairs. That means if the pipe is
wider, larger cross-section, it's also easier for the
current to flow, it's easier for the water to
flow. So that's also quite pleasing.
Ohm's Law, also, often holds for insulators,
which are not conductors, even though I have derived it
here for conductors, which have these free
electrons.
And so now, I want to make a
comparison between very good conductors, and very good
insulators. So I'll start off with a -- a
chunk of material , cross-sectional area A -- let's
take it one millimeter by one millimeter -- so A is ten to
the minus six square meters. So here I have a chunk of
material, and the length of that material L is one meter.
Put a potential difference over there, plus here,
and minus here. Current will start to flow in
this direction, electrons will flow in this
direction.
The question now is,
what is the resistance of this chunk of material?
Well, very easy. You take these equations,
you know L and A, so if I tell you what sigma is,
then you can immediately calculate what the resistance
is. So let's take,
first, a good conductor. Silver and gold and copper are
very good conductors.
They would have values of sigma, ten to the eight,
we just calculated for copper, you've seen in front of your
own eyes.
So that means rho would be ten
to the minus eight, it's one over sigma.
And so in this particular case, since A is ten to the minus
six, the resistance R is simply ten to
the sixth times rho. Because L is one meter.
So it's very easy -- resistance here, R, is ten to the minus two
ohms. One-hundredth of an ohm.
For this material if it were copper.
Let's now take a very good insulator.
Glass is an example. Quartz, porcelain,
very good insulators.
Now, sigma, the conductivity,
is extremely low. They vary somewhere from ten to
the minus twelve through ten to the minus sixteen.
So rho, now, the resistivity,
is something like ten to the twelve to twelve to the plus
sixteens, and if I take ten to the fourteen,
just I grab -- I have to grab a number -- then you'll find that
R, now, is ten to the twenty ohms.
A one with twenty zeros. That's an enormous resistance.
So you see the difference -- twenty-two orders of magnitude
difference between a good conductor and a good insulator.
And if I make this potential difference over the wire,
if I make that one volt, and if I apply Ohm's Law,
V equals I R, then I can also calculate the
current that is going to flow. If I R is one,
then the current here is hundred amperes,
and the current here is ten to the minus twenty amperes,
an insignificant current, ten to the minus twenty
amperes.
I first want to demonstrate to
you that Ohm's Law sometimes holds, I will do a
demonstration, whereby you have a voltage
supply -- put a V in here -- and we change the voltage in a
matter of a few seconds from zero to four volts.
This is the plus side, this is the minus side,
I have connected it here to a resistor which is fifty ohms --
we use this symbol for a resistor -- and here is a
current meter. And the current meter has
negligible resistance, so you can ignore that.
And I'm going to show you on an oscilloscope -- we've never
discussed an oscilloscope, but maybe we will in the future
-- I'm going to show you, they are projected -- the
voltage unintelligible go from zero to four,
versus the current. And so it will start here,
and by the time we reach four volts, then we would have
reached a current of four divided by fifty,
according to Ohm's Law, I will write down just four
divided by fifty amperes, which is point
oh eight amperes. And if Ohm's Law holds,
then you would find a straight line.
That's the whole idea about Ohm's Law, that the potential
difference, linearly proportional to the current.
You double the potential difference, your current
doubles.
So let's do that,
let's take a look at that, you're going to see that there
-- and I have to change my lights so
that you get a good shot at it -- oh, it's already going.
So you see, horizontally, we have the current,
and vertically, we have the voltage.
And so it takes about a second to go from zero to four -- so
this goes from zero to four volts -- and you'll see that the
current is beautifully linear. Yes, I'm blocking it -- oh,
no, it's my reflection, that's interesting.
Ohm's Law doesn't allow for that.
So you see how beautifully linear it is.
So now, you may have great confidence in Ohm's Law.
Don't have any confidence in Ohm's Law.
The conductivity sigma is a strong function of the
temperature. If you increase the
temperature, then the time tau between collisions goes down,
because the speed of these free electrons goes up.
It's a very strong function of temperature.
And so if tau goes down, then clearly,
what will happen is that the conductivity will go down.
And that means rho will go up. And so you get more resistance.
And so when you heat up a substance, the resistance goes
up.
A higher temperature,
higher resistance. So the moment that the
resistance R becomes a function of the
temperature, I call that a total breakdown
of V equals I R, a total breakdown of Ohm's Law.
If you look in your book, they say, "Oh,
no, no, no, that's not a breakdown.
You just have to adjust the re- the resistance for a different
temperature." Well, yes, that's an incredible poor
man's way of saving a law that is a very bad law.
Because the temperature itself is a function of current,
the higher the current the higher the temperature.
And so now, you get a ratio, V divided by I,
which is no longer constant. It becomes a function of the
current. That's the end of Ohm's Law.
And so I want to show you that if I do the same experiment that
I did here, but if I replace this by a light bulb of fifty
ohms -- it's a very small light bulb, resistance when it is hot
is fifty ohms, when it is cold,
it is seven ohms.
So R cold of the light bulb is
roughly seven ohms, I believe, but I know that when
it is hot, it's very close to the fifty ohms.
Think it's a little lower. What do you expect now?
Well, you expect now, that when the resistance is low
in the beginning, you get this,
and then when the resistance goes up, you're going to get
this. I may end up a little higher
current, because I think the resistance is a
little lower than fifty ohms. And if you see a curve like
this, that's not linear anymore.
So that's the end of Ohm's Law.
And that's what I want to show you now.
So, all I do is, here I have this little light
bulb -- for those of you who sit close, they can actually see
that light bulb start glowing, but that's not important,
I really want you to see that V. Versus I is no longer linear,
there you go. And you see,
every time you see this light bulb go on, it heats up,
and during the heating up, it, um, the resistance
increases. And it's the end of Ohm's Law,
for this light bulb, at least.
It was fine for the other resistor, but it was not fine
for this light bulb.
There is another way that I can
That is the resistivity, show you that Ohm's Law is not
always doing so well. I have a hundred twenty-five
volt power supply, so V is hundred and twenty-five
volts -- this is the potential difference -- and I have a light
bulb, you see it here, that's the light bulb -- the
resistance of the light bulb, cold, I believe,
is twenty-five ohms, and hot, is about two hundred
and fifty ohms. A huge difference.
So if the resistance -- if I. Take the cold resistance,
then I would get five amperes, but by the time that the bulb
is hot, I would only get half an ampere.
It's a huge difference.
And what I want to show you,
again with the oscilloscope, is the current as a function of
time. When you switch on a light
bulb, you would expect, if Ohm's Law holds,
that when you switch on the current -- or switch on the
voltage, I should say -- that you see this.
This is then your five amperes. And that it would stay there.
That's the whole idea. Namely, that the voltage
divided by the current remains a constant.
However, what you're going to see is like this.
Current goes up, but then the resistance goes
down, then the resistance goes up, when the current goes up,
the resistance goes up, and then therefore the current
will go down, and will level off at a level
which is substantially below this.
So you're looking there -- you're staring at the breakdown
of Ohm's Law.
And so that's what I want to
show you now. So, here we need a hundred and
twenty five volts -- and there is the light bulb,
and when I throw this switch, you will see the pattern of the
current versus time -- you will only see it once,
and then we freeze it with the oscilloscope -- turn this off --
so look closely, now.
There it is. Forget these little ripple that
you see on it, it has to do with the way that
we produce the hundred and twenty five volts.
And so you see here, horizontally,
time, the time between two adjacent vertical lines is
twenty milliseconds. And so, indeed,
very early on, the current surged toward -- to
a very high value, and then the filament heats up,
and so the resistance goes up, the light bulb,
and the current just goes back again.
From the far left to the far right on the screen is about two
hundred milliseconds.
That's about two tenths of a
second. And here you get a current
level which is way lower than what you get there.
That's a breakdown of Ohm's Law.
It is actually very nice that resistances go up with light
bulbs when the temperature goes up.
Because, suppose it were the other way around.
Suppose you turn on a light bulb, and the resistance would
go down. Light bulb got hot,
resistance goes down, that means the current goes up.
Instead of down, the current goes up.
That means it gets hotter. That means the resistance goes
even further down.
That means the current goes
even further up. And so what it would mean is
that every time you turn on a light bulb, it would,
right in front of your eyes, destruct itself.
That's not happening. It's the other way around.
So, in a way, it's fortunate that the
resistance goes up when the light bulbs get hot.
All right. Let's now be a little bit more
qualitative on some networks of resistors, and we'll have you do
a few problems like that, whereby we just will assume,
naively, that Ohm's Law holds.
In other words,
we will always assume that the values for the resistances that
we give you will not change. So we will assume that the heat
that is produced will not play any important role.
So we will just use Ohm's Law, for now, and if you can't use
it, we will be very specific about that.
So suppose I have here, between point A and point B,
suppose I have two resistors, R one and R two.
And suppose I apply a potential difference between A and B,
that this be plus, and this be minus,
and the potential difference is V.
And you know V, this is known,
I give you V, I gave you this resistance,
and I gave you that one. So I could ask you now,
what is the current that is going to flow?
I could also ask you, then, what is the potential
difference over this resistor alone --
which I will call V one -- and what is the potential difference
over the second resistor, which I call V two?
Very straightforward question. Well, you apply,
now, Ohm's Law, and so between A and B,
there are two resistors, in series.
So the current has to go through both,
and so the potential difference V, in Ohm's Law,
is now the total current times R one plus R two.
Suppose these two resistors were the same,
they had the same length, same cross-sectional area.
If you put two in series, you have twice the length.
Well, so, twice the length, remember, resistance is
linearly proportional with the length of a wire,
and so you add them up.
So now you know R one and you
know R two, you know V, so you already know the
current, very simple. You can also apply Ohm's Law,
as long as it holds, for this resistor alone.
So then you get that V one equals I times R one,
so now you have the voltage over this resistor,
and of course, V two must be the current I
times R two. And so you have solved your
problem. All the questions that I asked
you, you have the answers to.
We could now have a slightly
different problem, whereby point A is here,
but now we have a resistor here,
which is R one, and we have here,
R two. This is point B,
and this is R two. And the potential difference is
V, that is, again, given, and now I could ask you,
what, now, is the current that will flow here?
And then I can also ask you, what is the current that would
go through one -- resistor one, and what is the current that
could go through resistor two?
And I would allow you to use Ohm's Law.
So now you say, "Aha!
The potential difference from A. To B going this route,
that potential difference, is V, that's a given." So V
must now be I one times R one.
That's Ohm's Law,
for this upper branch. But, of course,
you can also go the lower branch.
So the same V is also I two times R two.
But whatever current comes in here must split up between these
two, think of it as water. You cannot get rid of charges.
The number of charges per second that flow into this
juncture continue on, and so I, the total current,
is I one plus I two. And so now,
you see, you have all the ingredients that you need to
solve for the current I -- for the current I one,
and for the current I two.
And you can turn this into an
industry, you can make extremely complicated networks of
resistors -- and if you were in course six, you should love it
-- I don't like it at all, so you don't have to worry
about it, you're not going to get very complicated resistor
net- networks from me -- but in course six,
you're going to see a lot of them.
They're going to throw them -- stuff them down your throat.
The conductivity of a substan- substance goes up if I can
increase the number of charge carriers.
If we have dry air, and it is cold,
then the resistivity of cold, dry air at
one atmosphere -- so rho for air, cold, dry,
one atmosphere -- cold means temperature that we have outside
-- it's about four times ten to the thirteen.
That is the resistivity of air. It is about what it is in
this room, maybe a little lower, because the temperature
is a little higher. If I heat it up -- the air --
then the conductivity will go up.
Resistivity will go down, because now,
I create oxygen and nitrogen ions by heating up the air.
Remember when we had this lightning, the unintelligible
came down, and we created a channel full of ions and
electrons, that had a very low resistivity,
a very high conductivity. And so what I want to
demonstrate to you, that when I create ions in this
room, that I can actually make the conductivity of air go up
tremendously.
Not only will the electrons
move, but also the ions, now, will start to move.
And the way I'm going to do that is, I'm going to put charge
on the electroscope -- oh, that is not so good --
no harm done. I'm going to put charge on the
electroscope, and you will see that the
conductivity of air is so poor that it will stay there for
hours. And then what I will do,
I will create ions in the vicinity of the electroscope.
But let's first put some charge on the electroscope.
I have here a glass rod and I'll put some charge on it.
OK, that's a lot of charge. And, uh, the r- the air is
quite dry, conductivity is very, very small, and so the charge
cannot go off through the air to the surroundings,
to the earth.
But now I'm going to create
ions there by heating it up, and I decided to do that with a
candle, because a candle is very romantic,
as we all know. So here I have this candle --
look how well the charge is holding, eh?
-- And here's my candle. And I will bring the candle --
oh, maybe twenty centimeters from the electroscope.
Look at it, look at it, already going.
It's about fifteen centimeters away.
I'll take my candle away, and it stops again.
So it's all due to the fact that I'm ionizing the air there,
creating free electrons as well as ions, and they both
participate now in the current, and the charge can flow away
from the electroscope through the earth, because the
conductivity now is so much higher.
I stop again, and it stops.
You see in front of your eyes how important the temperature
is, in this case, the presence of the ions in the
air. If I have clean,
distilled water -- I mean, clean water.
I don't mean the stuff that you get in Cambridge,
let alone did I mean the stuff that is in the Charles River,
I mean clean water, that has a pH of seven.
That means one out of ten to the seven of the water molecules
is ionized, H plus and O H.
Minus.
The conductivity, by the way, is not the result
of the free electrons,
but is really the result of these H plus and O H minus ions.
It's one of the cases whereby not the -- the electrons are
maj- the major responsibility for the current.
If I have add three percent of salt, in terms of weight,
then all that salt will ionize, so you get sodium plus and C L
minus ions, you increase the number of ions by an enormous
factor. And so the conductivity will
soar up by a factor of three hundred
thousand, or up to a million, because you increase the ions
by that amount. And so it's no surprise then,
for you, that the conductivity of seawater is a million times
higher -- think about it, a million times higher -- than
the conductivity of distilled water.
And I would like to give you the number for water --
so this is distilled water -- that is about two times ten to
the fifth ohm-meters. There is another way that I can
That is the resistivity, two times ten to the five
oh-meters.
I have here,
a bucket of distilled water. I'll make a drawing for you on
the blackboard there. So here is a bucket of
distilled water, and in there,
is a copper plate, and another copper plate,
and here is a light bulb, and this will go straight to
the outlet [wssshhht], stick it in,
hundred ten volts. This light bulb has eight
hundred ohm resistance when it is hot.
You see the light bulb here.
You can calculate what this
resistance is between the two plates, that's easy,
you have all the tools now. If you know the distance,
it's about twenty centimeters, and you know the surface area
of the plates, because remember,
the resistance is inversely proportional with A,
so you have to take that into account -- and you take the
resistivity of water into account, it's a trivial
calculation, you can calculate what the resistance is of this
portion here. And I found that this
resistance here is about two megaohms.
Two million ohms. So, when I plug this into a
wall, the current that will flow is extremely low,
because it has to go through the eight hundred ohms,
and through the two megaohms.
So you won't see anything,
the light bulb will not show any
light. But now, if I -- put salt in
here, if I really manage to put three percent in weight salt in
here, then this two megaohm will go down to two ohms,
a million times less. So now, the light bulb will be
happy like a clam at high tide, because two ohms here,
plus the eight hundred, the two is insignificant.
And this is what I want to -- to demonstrate to you now,
the enormous importance of
increasing ions. I increased ions here by
heating the air, now I'm going to increase the
ions by adding salt.
And so the first thing that I
will do is, I will stick this in here.
There's the light bulb. And I make a daring prediction
that you will see nothing. There we go.
Nothing. Isn't that amazing?
You didn't expect that, right?
Physics works.
You see nothing.
If I take the plates out, and touch them with each other,
what will happen? There you go.
But this water has such a huge resistance that the current is
too low. Well, let's add some -- not
pepper -- add some salt. Yes, there's salt in there.
It's about as much as I would put on my eggs in the morning --
stir a little -- ah, hey, look at that.
Isn't that amazing? And when I bring them closer
together, it will become even brighter, because L is now
smaller, the distance is smaller.
I bring them farther apart, it's amazing.
Just a teeny, weeny little bit of salt,
about as much as I use on my egg, let alone -- what the hell,
let's put everything in there -- that's a unintelligible I put
everything, then, of course, you go almost down
to the two ohms, and the light bulb will be just
burning normally. But even with that little bit
of salt, you saw the huge difference.
My body is a fairly good conductor -- yours too,
we all came out of the sea -- so we are almost
all water -- and therefore, when we do experiments with
little charge, like the van der Graf,
being a student, then we have to insulate
ourselves very carefully, putting glass plates under us,
or plastic stools, to prevent that the charge runs
down to the earth.
In fact, the resistance,
my resistance between my body and the earth is largely
dictated by the soles of my shoe,
not by my body, not by my skin.
But if you look at my soles, then you get something like
this, and it has a certain thickness, and this,
maybe one centimeter. This, now, is L in my
calculation for the resistance, because current may flow in
this direction, so that's L.
Well, how large is my foot? Let's say it's one foot long --
no pun implied -- and let's say it's about ten centimeters wide.
So you can calculate what the surface area A is,
you know what L is, and if you know,
now what the resistivity is for my sole, I can make a rough
guess, I looked up the material, and I found that the
resistivity is about ten to the tenth.
So I can now calculate what the resistance is in this
direction. And I found that that
resistance then, putting in the numbers,
is about ten billion ohm. And you will say,
"Wow!" Oh, it's four, actually.
Well, big deal.
Four billion ohm.
So you will say, "That's enormous resistance!"
Well, first of all, I'm walking on two feet,
not on one, so if I would be standing one the whole lecture,
it would probably be four billion, but if I have two feet
on the ground, it's really two billion,
you will say, "Well, that's still extremely
large!" Well, it may look large,
but it really isn't, because all the experiments
that we are doing here in twenty six one hundred,
you're dealing with very small amounts of charge.
Even if you take the van der Graff -- the van der Graff,
say, has two hundred thousand volts -- and let's assume that
my resistance is two times ten to the nine ohms,
two feet on the ground. So when I touch the van der
Graff, the current that would flow,
according to Ohm's Law, would be hundred microamperes.
That means, in one second, I can take hundred
microCoulombs of the van der Graff, but the van der Graff has
only ten microCoulombs on in. So the resistance of four
billion or two billion ohms is way too low for these
experiments that we have been doing in twenty six one hundred,
and that's why we use these plastic stools,
and we use these glass plates in order to make sure that the
current is not draining off the the
charge that we need for the experiments.
I want to demonstrate that to you, that, indeed,
even with my shoes on -- that means, even with my two billion
ohm resistance to the ground -- that it will be very difficult
for me, for instance, to keep charge on an
electroscope. I'm going to put charge on this
electroscope by scuffing my feet.
But, since I keep my -- I have my shoes on, I'm not standing on
the glass plate, the charge will flow through
me.
You can apply Ohm's Law.
And you will see that as I do this -- I'm scuffing my feet now
-- that I can only keep that electroscope charged as long as
I keep scuffing. But the moment that I stop
scuffing, it's gone. Start scuffing again,
that's fine, but the moment that I
stop scuffing, it goes off again.
Even though this resistance is something like two billion ohms.
Let alone if I take my shoes off.
I apologize for that. If now I scuff,
I can't even get any charge on the electroscope,
because now, the resistance is so
ridiculously low, I don't even have the two
billion ohms, I can't even put any charge on
the electroscope.
It's always very difficult for
us to do these experiments unless we
insulate ourselves very well. And if, somehow,
the weather is a little damp, we can very thin films of water
onto our tools, and then the current can flow
off just through these very thin layers of water.
That's why we always like to do these experiments in winter,
so that the conductivity of the air is very low,
no water anywhere. Here you see a slide of a
robbery. I have scuffed my feet across
the rug, and I am armed with a static charge.
Hand over all your money, or I'll touch your nose.
This person either never took eight oh two,
or he is wearing very, very special shoes.
See you on Wednesday..Putri LaksmiDecember 10, 2017AdminBandung Indonesia
When positive charges move in
this direction, then per definition,
we say the current goes in this direction.
When negative charges go in this direction,
we also say the current goes in that direction,
that's just our convention. If I apply a potential
difference over a conductor, then I'm going to create an
electric field in that conductor.
And the electrons -- there are free electrons in a conductor --
they can move, but the ions cannot move,
because they are frozen into the solid, into the crystal.
And so when a current flows in a conductor, it's always the
electrons that are responsible for the current.
The electrons fuel the electric fields, and then the electrons
try to make the electric field zero, but they can't succeed,
because we keep the potential difference over the conductor.
Often, there is a linear relationship between current and
the potential, in which case,
we talk about Ohm's Law. Now, I will try to derive Ohm's
Law in a very crude way,
a poor man's version, and not really one hundred
percent kosher, it requires quantum mechanics,
which is beyond the course -- beyond this course -- but I will
do a job that still gives us some interesting insight into
Ohm's Law. If I start off with a
conductor, for instance, copper, at room temperature,
three hundred degrees Kelvin, the free electrons in copper
have a speed, an average speed of about a
million meters per second.
So this is the average speed of
those free electrons, about a million meters per
second. This in all directions.
It's a chaotic motion. It's a thermal motion,
it's due to the temperature. The time between collisions --
time between the collisions -- and this is a collision of the
free electron with the atoms -- is approximately -- I call it
tau -- is about three times ten to the
minus fourteen seconds.
No surprise,
because the speed is enormously high.
And the number of free electrons in copper per cubic
meter, I call that number N, is about ten to the
twenty-nine. There's about one free electron
for every atom. So we get twen- ten to the
twenty-nine free electrons per cubic meter.
So now imagine that I apply a potential difference piece of
copper -- or any conductor, for that matter -- then the
electrons will experience a force which is the charge of the
electron, that's my little E. Times the electric field that
I'm creating, because I apply a potential
difference.
I realize that the force and
the electric field are in opposite directions for
electrons, but that's a detail, I'm interested
in the magnitudes only. And so now these electrons will
experience an acceleration, which is the force divided by
the mass of the electron, and so they will pick up,
eh, speed, between these colli- collisions, which we call the
drift velocity, which is A times tau,
it's just eight oh one. And so A equals F divided by M.
E F is in the A, so we get E times E divided by
the mass of the electrons, times tau.
And that is the the drift velocity.
When the electric field goes up, the drift velocity goes up,
so the electrons move faster in the direction opposite to the
current. If the time between collisions
gets larger, they -- the acceleration lasts longer,
so also, they pick up a larger speed, so that's intuitively
pleasing.
If we take a specific case,
and I take, for instance, copper,
and I apply over the -- over a wire -- let's say the wire has a
length of 10 meters -- I apply a potential difference I call
delta V, but I could have said just V -- I apply there a
potential difference of ten volts, then the electric field
-- inside the conductor, now -- is about one volt per
meter. And so I can calculate,
now, for that specific case, I can calculate what the drift
velocity would be. So the drift velocity of those
free electrons would be the charge of the electron,
which is one point six times ten to the minus nineteen
Coulombs. The E field is one,
so I can forget about that.
Tau is three times ten to the
minus fourteen, as long as I'm room
temperature, and the mass of the electron is about ten to the
minus thirty kilograms. And so, if I didn't slip up,
I found that this is five times ten to the minus three meters
per second, which is half a centimeter per second.
So imagine, due to the thermal motion, these free electrons
move with a million meters per second.
But due to this electric field, they only advance along the
wire slowly, like a snail, with a speed on average of half
a centimeter per second. And that goes very much against
your and my own intuition, but this is the way it is.
I mean, a turtle would go faster than these electrons.
To go along a ten-meter wire would take half hour.
Something that you never thought of.
That it would take a half hour for these electrons to go along
the wire if you apply potential difference of ten volts,
copper ten meters long. Now, I want to massage this
further, and see whether we can somehow
squeeze out Ohm's Law, which is the linear relation
between the potential and the current.
So let me start off with a wire which has a cross-section A,
and it has a length L, and I put a potential
difference over the wire,
plus here, and minus there, potential V,
so I would get a current in this direction,
that's our definition of current, going from plus to
minus.
The electrons,
of course, are moving in this direction, with the drift
velocity. And so the electric field in
here, which is in this direction, that electric field
is approximately V divided by L, potential difference divided by
distance. In one second,
these free electrons will move from left to right over a
distance V D meters. So if I make any cross-section
through this wire, anywhere, I can calculate how
many electrons pass through that cross-section in one second.
In one second, the volume that passes through
here, the volume is V D times A.
But the number of free
electrons per cubic meter is called N, so this is now the
number of free electrons that passes, per second,
through any cross-section. And each electron has a charge
E, and so this is the current that will flow.
The current, of course, is in this
direction, but that's a detail. If I now substitute the drift
velocity, which we have here, I substitute that in there,
but then I find that the current -- I get a E squared,
the charge squared, I get N, I get tau,
I get downstairs, the mass of the electron,
and then I get A times the electric field E.
Because I have here, is electric field E.
When you look at this here, that really depends only on the
properties of by substance, for a given temperature.
And we give that a name. We call this sigma,
which is called conductivity.
Conductivity.
If I calculate, for copper, the conductivity,
at room temperature, that's very easy,
because I've given you what N. Is, on the blackboard there,
ten to the twenty-nine, you know what tau is at room
temperature, three times ten to the minus fourteen,
so for copper, at room temperature,
you will find about ten to the eighth.
You will see more values fro sigma later on during this
course. This is in SI units.
I can massage this a little further, because E is V divided
by L, and so I can write now that the
current is that sigma times A. Times V divided by L.
I can write it down a little bit differently,
I can say V, therefore, equals L divided by
sigma A, times I.
And now, you're staring at
Ohm's Law, whether you like it or not,
because this is what we call the resistance,
capital R. We often write down rho for one
over sigma, and rho is called the resistivity.
So either one will do. So you can also write down --
you can write down V equals I R, and this R, then,
is either L divided by sigma A, or L times rho -- let me make
it a nicer rho -- divided by A. That's the same thing.
The units for resistance R is volts per ampere,
but we call that ohm.
And so the unit for R is ohm.
And so if you want to know what the
unit for rho and sigma is, that follows immediately from
the equations. The unit for rho is then
ohm-meters. So we have derived the
resistance here in terms of the dimensions -- namely,
the length and the cross-section -- but also in
terms of the physics on an atomic scale,
which, all by itself, is interesting.
If you look at the resistance, you see it is proportional with
the length of your wire through
which you drive a current. Think of this as water trying
to go through a pipe.
If you make the pipe longer,
the resistance goes up, so that's very intuitively
pleasing. Notice that you have A
downstairs. That means if the pipe is
wider, larger cross-section, it's also easier for the
current to flow, it's easier for the water to
flow. So that's also quite pleasing.
Ohm's Law, also, often holds for insulators,
which are not conductors, even though I have derived it
here for conductors, which have these free
electrons.
And so now, I want to make a
comparison between very good conductors, and very good
insulators. So I'll start off with a -- a
chunk of material , cross-sectional area A -- let's
take it one millimeter by one millimeter -- so A is ten to
the minus six square meters. So here I have a chunk of
material, and the length of that material L is one meter.
Put a potential difference over there, plus here,
and minus here. Current will start to flow in
this direction, electrons will flow in this
direction.
The question now is,
what is the resistance of this chunk of material?
Well, very easy. You take these equations,
you know L and A, so if I tell you what sigma is,
then you can immediately calculate what the resistance
is. So let's take,
first, a good conductor. Silver and gold and copper are
very good conductors.
They would have values of sigma, ten to the eight,
we just calculated for copper, you've seen in front of your
own eyes.
So that means rho would be ten
to the minus eight, it's one over sigma.
And so in this particular case, since A is ten to the minus
six, the resistance R is simply ten to
the sixth times rho. Because L is one meter.
So it's very easy -- resistance here, R, is ten to the minus two
ohms. One-hundredth of an ohm.
For this material if it were copper.
Let's now take a very good insulator.
Glass is an example. Quartz, porcelain,
very good insulators.
Now, sigma, the conductivity,
is extremely low. They vary somewhere from ten to
the minus twelve through ten to the minus sixteen.
So rho, now, the resistivity,
is something like ten to the twelve to twelve to the plus
sixteens, and if I take ten to the fourteen,
just I grab -- I have to grab a number -- then you'll find that
R, now, is ten to the twenty ohms.
A one with twenty zeros. That's an enormous resistance.
So you see the difference -- twenty-two orders of magnitude
difference between a good conductor and a good insulator.
And if I make this potential difference over the wire,
if I make that one volt, and if I apply Ohm's Law,
V equals I R, then I can also calculate the
current that is going to flow. If I R is one,
then the current here is hundred amperes,
and the current here is ten to the minus twenty amperes,
an insignificant current, ten to the minus twenty
amperes.
I first want to demonstrate to
you that Ohm's Law sometimes holds, I will do a
demonstration, whereby you have a voltage
supply -- put a V in here -- and we change the voltage in a
matter of a few seconds from zero to four volts.
This is the plus side, this is the minus side,
I have connected it here to a resistor which is fifty ohms --
we use this symbol for a resistor -- and here is a
current meter. And the current meter has
negligible resistance, so you can ignore that.
And I'm going to show you on an oscilloscope -- we've never
discussed an oscilloscope, but maybe we will in the future
-- I'm going to show you, they are projected -- the
voltage unintelligible go from zero to four,
versus the current. And so it will start here,
and by the time we reach four volts, then we would have
reached a current of four divided by fifty,
according to Ohm's Law, I will write down just four
divided by fifty amperes, which is point
oh eight amperes. And if Ohm's Law holds,
then you would find a straight line.
That's the whole idea about Ohm's Law, that the potential
difference, linearly proportional to the current.
You double the potential difference, your current
doubles.
So let's do that,
let's take a look at that, you're going to see that there
-- and I have to change my lights so
that you get a good shot at it -- oh, it's already going.
So you see, horizontally, we have the current,
and vertically, we have the voltage.
And so it takes about a second to go from zero to four -- so
this goes from zero to four volts -- and you'll see that the
current is beautifully linear. Yes, I'm blocking it -- oh,
no, it's my reflection, that's interesting.
Ohm's Law doesn't allow for that.
So you see how beautifully linear it is.
So now, you may have great confidence in Ohm's Law.
Don't have any confidence in Ohm's Law.
The conductivity sigma is a strong function of the
temperature. If you increase the
temperature, then the time tau between collisions goes down,
because the speed of these free electrons goes up.
It's a very strong function of temperature.
And so if tau goes down, then clearly,
what will happen is that the conductivity will go down.
And that means rho will go up. And so you get more resistance.
And so when you heat up a substance, the resistance goes
up.
A higher temperature,
higher resistance. So the moment that the
resistance R becomes a function of the
temperature, I call that a total breakdown
of V equals I R, a total breakdown of Ohm's Law.
If you look in your book, they say, "Oh,
no, no, no, that's not a breakdown.
You just have to adjust the re- the resistance for a different
temperature." Well, yes, that's an incredible poor
man's way of saving a law that is a very bad law.
Because the temperature itself is a function of current,
the higher the current the higher the temperature.
And so now, you get a ratio, V divided by I,
which is no longer constant. It becomes a function of the
current. That's the end of Ohm's Law.
And so I want to show you that if I do the same experiment that
I did here, but if I replace this by a light bulb of fifty
ohms -- it's a very small light bulb, resistance when it is hot
is fifty ohms, when it is cold,
it is seven ohms.
So R cold of the light bulb is
roughly seven ohms, I believe, but I know that when
it is hot, it's very close to the fifty ohms.
Think it's a little lower. What do you expect now?
Well, you expect now, that when the resistance is low
in the beginning, you get this,
and then when the resistance goes up, you're going to get
this. I may end up a little higher
current, because I think the resistance is a
little lower than fifty ohms. And if you see a curve like
this, that's not linear anymore.
So that's the end of Ohm's Law.
And that's what I want to show you now.
So, all I do is, here I have this little light
bulb -- for those of you who sit close, they can actually see
that light bulb start glowing, but that's not important,
I really want you to see that V. Versus I is no longer linear,
there you go. And you see,
every time you see this light bulb go on, it heats up,
and during the heating up, it, um, the resistance
increases. And it's the end of Ohm's Law,
for this light bulb, at least.
It was fine for the other resistor, but it was not fine
for this light bulb.
There is another way that I can
That is the resistivity, show you that Ohm's Law is not
always doing so well. I have a hundred twenty-five
volt power supply, so V is hundred and twenty-five
volts -- this is the potential difference -- and I have a light
bulb, you see it here, that's the light bulb -- the
resistance of the light bulb, cold, I believe,
is twenty-five ohms, and hot, is about two hundred
and fifty ohms. A huge difference.
So if the resistance -- if I. Take the cold resistance,
then I would get five amperes, but by the time that the bulb
is hot, I would only get half an ampere.
It's a huge difference.
And what I want to show you,
again with the oscilloscope, is the current as a function of
time. When you switch on a light
bulb, you would expect, if Ohm's Law holds,
that when you switch on the current -- or switch on the
voltage, I should say -- that you see this.
This is then your five amperes. And that it would stay there.
That's the whole idea. Namely, that the voltage
divided by the current remains a constant.
However, what you're going to see is like this.
Current goes up, but then the resistance goes
down, then the resistance goes up, when the current goes up,
the resistance goes up, and then therefore the current
will go down, and will level off at a level
which is substantially below this.
So you're looking there -- you're staring at the breakdown
of Ohm's Law.
And so that's what I want to
show you now. So, here we need a hundred and
twenty five volts -- and there is the light bulb,
and when I throw this switch, you will see the pattern of the
current versus time -- you will only see it once,
and then we freeze it with the oscilloscope -- turn this off --
so look closely, now.
There it is. Forget these little ripple that
you see on it, it has to do with the way that
we produce the hundred and twenty five volts.
And so you see here, horizontally,
time, the time between two adjacent vertical lines is
twenty milliseconds. And so, indeed,
very early on, the current surged toward -- to
a very high value, and then the filament heats up,
and so the resistance goes up, the light bulb,
and the current just goes back again.
From the far left to the far right on the screen is about two
hundred milliseconds.
That's about two tenths of a
second. And here you get a current
level which is way lower than what you get there.
That's a breakdown of Ohm's Law.
It is actually very nice that resistances go up with light
bulbs when the temperature goes up.
Because, suppose it were the other way around.
Suppose you turn on a light bulb, and the resistance would
go down. Light bulb got hot,
resistance goes down, that means the current goes up.
Instead of down, the current goes up.
That means it gets hotter. That means the resistance goes
even further down.
That means the current goes
even further up. And so what it would mean is
that every time you turn on a light bulb, it would,
right in front of your eyes, destruct itself.
That's not happening. It's the other way around.
So, in a way, it's fortunate that the
resistance goes up when the light bulbs get hot.
All right. Let's now be a little bit more
qualitative on some networks of resistors, and we'll have you do
a few problems like that, whereby we just will assume,
naively, that Ohm's Law holds.
In other words,
we will always assume that the values for the resistances that
we give you will not change. So we will assume that the heat
that is produced will not play any important role.
So we will just use Ohm's Law, for now, and if you can't use
it, we will be very specific about that.
So suppose I have here, between point A and point B,
suppose I have two resistors, R one and R two.
And suppose I apply a potential difference between A and B,
that this be plus, and this be minus,
and the potential difference is V.
And you know V, this is known,
I give you V, I gave you this resistance,
and I gave you that one. So I could ask you now,
what is the current that is going to flow?
I could also ask you, then, what is the potential
difference over this resistor alone --
which I will call V one -- and what is the potential difference
over the second resistor, which I call V two?
Very straightforward question. Well, you apply,
now, Ohm's Law, and so between A and B,
there are two resistors, in series.
So the current has to go through both,
and so the potential difference V, in Ohm's Law,
is now the total current times R one plus R two.
Suppose these two resistors were the same,
they had the same length, same cross-sectional area.
If you put two in series, you have twice the length.
Well, so, twice the length, remember, resistance is
linearly proportional with the length of a wire,
and so you add them up.
So now you know R one and you
know R two, you know V, so you already know the
current, very simple. You can also apply Ohm's Law,
as long as it holds, for this resistor alone.
So then you get that V one equals I times R one,
so now you have the voltage over this resistor,
and of course, V two must be the current I
times R two. And so you have solved your
problem. All the questions that I asked
you, you have the answers to.
We could now have a slightly
different problem, whereby point A is here,
but now we have a resistor here,
which is R one, and we have here,
R two. This is point B,
and this is R two. And the potential difference is
V, that is, again, given, and now I could ask you,
what, now, is the current that will flow here?
And then I can also ask you, what is the current that would
go through one -- resistor one, and what is the current that
could go through resistor two?
And I would allow you to use Ohm's Law.
So now you say, "Aha!
The potential difference from A. To B going this route,
that potential difference, is V, that's a given." So V
must now be I one times R one.
That's Ohm's Law,
for this upper branch. But, of course,
you can also go the lower branch.
So the same V is also I two times R two.
But whatever current comes in here must split up between these
two, think of it as water. You cannot get rid of charges.
The number of charges per second that flow into this
juncture continue on, and so I, the total current,
is I one plus I two. And so now,
you see, you have all the ingredients that you need to
solve for the current I -- for the current I one,
and for the current I two.
And you can turn this into an
industry, you can make extremely complicated networks of
resistors -- and if you were in course six, you should love it
-- I don't like it at all, so you don't have to worry
about it, you're not going to get very complicated resistor
net- networks from me -- but in course six,
you're going to see a lot of them.
They're going to throw them -- stuff them down your throat.
The conductivity of a substan- substance goes up if I can
increase the number of charge carriers.
If we have dry air, and it is cold,
then the resistivity of cold, dry air at
one atmosphere -- so rho for air, cold, dry,
one atmosphere -- cold means temperature that we have outside
-- it's about four times ten to the thirteen.
That is the resistivity of air. It is about what it is in
this room, maybe a little lower, because the temperature
is a little higher. If I heat it up -- the air --
then the conductivity will go up.
Resistivity will go down, because now,
I create oxygen and nitrogen ions by heating up the air.
Remember when we had this lightning, the unintelligible
came down, and we created a channel full of ions and
electrons, that had a very low resistivity,
a very high conductivity. And so what I want to
demonstrate to you, that when I create ions in this
room, that I can actually make the conductivity of air go up
tremendously.
Not only will the electrons
move, but also the ions, now, will start to move.
And the way I'm going to do that is, I'm going to put charge
on the electroscope -- oh, that is not so good --
no harm done. I'm going to put charge on the
electroscope, and you will see that the
conductivity of air is so poor that it will stay there for
hours. And then what I will do,
I will create ions in the vicinity of the electroscope.
But let's first put some charge on the electroscope.
I have here a glass rod and I'll put some charge on it.
OK, that's a lot of charge. And, uh, the r- the air is
quite dry, conductivity is very, very small, and so the charge
cannot go off through the air to the surroundings,
to the earth.
But now I'm going to create
ions there by heating it up, and I decided to do that with a
candle, because a candle is very romantic,
as we all know. So here I have this candle --
look how well the charge is holding, eh?
-- And here's my candle. And I will bring the candle --
oh, maybe twenty centimeters from the electroscope.
Look at it, look at it, already going.
It's about fifteen centimeters away.
I'll take my candle away, and it stops again.
So it's all due to the fact that I'm ionizing the air there,
creating free electrons as well as ions, and they both
participate now in the current, and the charge can flow away
from the electroscope through the earth, because the
conductivity now is so much higher.
I stop again, and it stops.
You see in front of your eyes how important the temperature
is, in this case, the presence of the ions in the
air. If I have clean,
distilled water -- I mean, clean water.
I don't mean the stuff that you get in Cambridge,
let alone did I mean the stuff that is in the Charles River,
I mean clean water, that has a pH of seven.
That means one out of ten to the seven of the water molecules
is ionized, H plus and O H.
Minus.
The conductivity, by the way, is not the result
of the free electrons,
but is really the result of these H plus and O H minus ions.
It's one of the cases whereby not the -- the electrons are
maj- the major responsibility for the current.
If I have add three percent of salt, in terms of weight,
then all that salt will ionize, so you get sodium plus and C L
minus ions, you increase the number of ions by an enormous
factor. And so the conductivity will
soar up by a factor of three hundred
thousand, or up to a million, because you increase the ions
by that amount. And so it's no surprise then,
for you, that the conductivity of seawater is a million times
higher -- think about it, a million times higher -- than
the conductivity of distilled water.
And I would like to give you the number for water --
so this is distilled water -- that is about two times ten to
the fifth ohm-meters. There is another way that I can
That is the resistivity, two times ten to the five
oh-meters.
I have here,
a bucket of distilled water. I'll make a drawing for you on
the blackboard there. So here is a bucket of
distilled water, and in there,
is a copper plate, and another copper plate,
and here is a light bulb, and this will go straight to
the outlet [wssshhht], stick it in,
hundred ten volts. This light bulb has eight
hundred ohm resistance when it is hot.
You see the light bulb here.
You can calculate what this
resistance is between the two plates, that's easy,
you have all the tools now. If you know the distance,
it's about twenty centimeters, and you know the surface area
of the plates, because remember,
the resistance is inversely proportional with A,
so you have to take that into account -- and you take the
resistivity of water into account, it's a trivial
calculation, you can calculate what the resistance is of this
portion here. And I found that this
resistance here is about two megaohms.
Two million ohms. So, when I plug this into a
wall, the current that will flow is extremely low,
because it has to go through the eight hundred ohms,
and through the two megaohms.
So you won't see anything,
the light bulb will not show any
light. But now, if I -- put salt in
here, if I really manage to put three percent in weight salt in
here, then this two megaohm will go down to two ohms,
a million times less. So now, the light bulb will be
happy like a clam at high tide, because two ohms here,
plus the eight hundred, the two is insignificant.
And this is what I want to -- to demonstrate to you now,
the enormous importance of
increasing ions. I increased ions here by
heating the air, now I'm going to increase the
ions by adding salt.
And so the first thing that I
will do is, I will stick this in here.
There's the light bulb. And I make a daring prediction
that you will see nothing. There we go.
Nothing. Isn't that amazing?
You didn't expect that, right?
Physics works.
You see nothing.
If I take the plates out, and touch them with each other,
what will happen? There you go.
But this water has such a huge resistance that the current is
too low. Well, let's add some -- not
pepper -- add some salt. Yes, there's salt in there.
It's about as much as I would put on my eggs in the morning --
stir a little -- ah, hey, look at that.
Isn't that amazing? And when I bring them closer
together, it will become even brighter, because L is now
smaller, the distance is smaller.
I bring them farther apart, it's amazing.
Just a teeny, weeny little bit of salt,
about as much as I use on my egg, let alone -- what the hell,
let's put everything in there -- that's a unintelligible I put
everything, then, of course, you go almost down
to the two ohms, and the light bulb will be just
burning normally. But even with that little bit
of salt, you saw the huge difference.
My body is a fairly good conductor -- yours too,
we all came out of the sea -- so we are almost
all water -- and therefore, when we do experiments with
little charge, like the van der Graf,
being a student, then we have to insulate
ourselves very carefully, putting glass plates under us,
or plastic stools, to prevent that the charge runs
down to the earth.
In fact, the resistance,
my resistance between my body and the earth is largely
dictated by the soles of my shoe,
not by my body, not by my skin.
But if you look at my soles, then you get something like
this, and it has a certain thickness, and this,
maybe one centimeter. This, now, is L in my
calculation for the resistance, because current may flow in
this direction, so that's L.
Well, how large is my foot? Let's say it's one foot long --
no pun implied -- and let's say it's about ten centimeters wide.
So you can calculate what the surface area A is,
you know what L is, and if you know,
now what the resistivity is for my sole, I can make a rough
guess, I looked up the material, and I found that the
resistivity is about ten to the tenth.
So I can now calculate what the resistance is in this
direction. And I found that that
resistance then, putting in the numbers,
is about ten billion ohm. And you will say,
"Wow!" Oh, it's four, actually.
Well, big deal.
Four billion ohm.
So you will say, "That's enormous resistance!"
Well, first of all, I'm walking on two feet,
not on one, so if I would be standing one the whole lecture,
it would probably be four billion, but if I have two feet
on the ground, it's really two billion,
you will say, "Well, that's still extremely
large!" Well, it may look large,
but it really isn't, because all the experiments
that we are doing here in twenty six one hundred,
you're dealing with very small amounts of charge.
Even if you take the van der Graff -- the van der Graff,
say, has two hundred thousand volts -- and let's assume that
my resistance is two times ten to the nine ohms,
two feet on the ground. So when I touch the van der
Graff, the current that would flow,
according to Ohm's Law, would be hundred microamperes.
That means, in one second, I can take hundred
microCoulombs of the van der Graff, but the van der Graff has
only ten microCoulombs on in. So the resistance of four
billion or two billion ohms is way too low for these
experiments that we have been doing in twenty six one hundred,
and that's why we use these plastic stools,
and we use these glass plates in order to make sure that the
current is not draining off the the
charge that we need for the experiments.
I want to demonstrate that to you, that, indeed,
even with my shoes on -- that means, even with my two billion
ohm resistance to the ground -- that it will be very difficult
for me, for instance, to keep charge on an
electroscope. I'm going to put charge on this
electroscope by scuffing my feet.
But, since I keep my -- I have my shoes on, I'm not standing on
the glass plate, the charge will flow through
me.
You can apply Ohm's Law.
And you will see that as I do this -- I'm scuffing my feet now
-- that I can only keep that electroscope charged as long as
I keep scuffing. But the moment that I stop
scuffing, it's gone. Start scuffing again,
that's fine, but the moment that I
stop scuffing, it goes off again.
Even though this resistance is something like two billion ohms.
Let alone if I take my shoes off.
I apologize for that. If now I scuff,
I can't even get any charge on the electroscope,
because now, the resistance is so
ridiculously low, I don't even have the two
billion ohms, I can't even put any charge on
the electroscope.
It's always very difficult for
us to do these experiments unless we
insulate ourselves very well. And if, somehow,
the weather is a little damp, we can very thin films of water
onto our tools, and then the current can flow
off just through these very thin layers of water.
That's why we always like to do these experiments in winter,
so that the conductivity of the air is very low,
no water anywhere. Here you see a slide of a
robbery. I have scuffed my feet across
the rug, and I am armed with a static charge.
Hand over all your money, or I'll touch your nose.
This person either never took eight oh two,
or he is wearing very, very special shoes.
See you on Wednesday..
"Take a deep breath, (Music starts) get ready for one of the most hypnotic things you'll ever see in a science class. Have you heard that heat rises? Well, here you can see it's true for yourself. I've got some food coloring on the bottom of a plastic container, and there's a hot mug right underneath the red food coloring. As it's heated, the water rises.
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In essence, electrical substations consist of power transformers, circuit breakers, ... ... And secondary systems for protection, load control and metering. The input signals for these secondary systems are provided by the CTs and VTs ...
Most of us don't think much
In 2011, an international team of four astronomers
Thomas Alva Edison... Boys! I trust you brought
If you've been invested in manga or anime for any length of time Chances are, you've at some point fallen in love with a title from Shonen Jump The now legendary publication first began in 1968 and since then has consistently published titles both widely popular and critically acclaimed One such title was 2008's meta-fictional Bakuman A series about a young artist-writer duo trying to get their manga published in a fictional version of Shonen Jump while the actual manga itself was published in Shonen Jump in real life It gave a fascinating inside into how the legendary publication worked as each of the character fight for the number 1 spot in the Shonen Jump Weekly Popularity Polls which was a survey sent out to the readers of Jump, asking to rate their favorite titles from best to worst With popular series regularly receiving anime adaptation, featured films, and merchandise while those that scored low quickly disappearing from its pages While Bakuman ended in 2012, the same weekly war still takes place in Shonen Jump today and after re-reading a little Bakuman recently I've been wondering: What are the popular titles in Jump right now? And how is the magazine itself doing? In other words, what is the current state of Shonen Jump The best place we could start with this question is with our old friend, the Shonen Jump ranking data If you'd like to see a full breakdown on how I came to these figures, just go to my following Bleach video But suffice to say, it's a pretty arduous task involving a lot of numbers and spreadsheets based of the previously mentioned ranking of the Shonen Jump titles as seen in their index This graph represents the performance of Shonen Jump top 10 manga in 2016 and if we average them out of the course of the year, we got a list that looks a little like this At number 10, we have World Trigger. A sci-fi battle series which I have not yet have a chance to read But it's apparently pretty good but was also unfortunately the subject of a pretty lackluster anime adaptation Number 9 is the Disastrous Life of Saiki K. A gag manga about a high-schooler with psychic powers trying and failing to live a normal life At number 8, we have Samon-kun wa Summoner A gag/vaguely action-oriented series about a highschool boy adept at summoning demons and tormenting his friends In at number 7, we have Food Wars. A rather beautifully illustrated battle/cooking manga with an extreme penchant for fanservice In at number 6, we have Hanamaru Zumo I've only had the chance to read the first couple of chapters in this one, but what really stands out is the spectacular artwork really making the sumo matches feel like intense, desperate struggles Coming in at number 5, we have the Promised Neverland which chronicles the life of a group of young children growing up in an orphanage, where things are...
The allure of sun, sand and the ocean are synonymous with summer. The beach can provide us with a calm, peaceful retreat, playful childhood memories or an adventurous outing. Beaches are living, constantly changing ecosystems, but a simple shift in wind direction can transform tranquil lapping waves into a roaring intense surf. When the waves get large and a surf forms, strong rip currents will forms as well, creating dangerous conditions for swimmers.
You might have heard them referred to as undertow
Okay in today's video I am going to go
Let's explore the repercussions
When positive charges move in