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Energy & Electricity in Science : How Does an Electric Motor Work?

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    Hi, I'm Steve Jones and I'm going to explain
    how an electric motor works. Now I've drawn
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    this diagram, it looks rather complicated
    but it isn't really that complicated. There
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    are two main elements. The first is this pair
    of magnets, one with a north here, the other
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    with a south here. These are usually permanent
    magnets on small motors, but on big motors
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    they are not. The second main element is this
    coil here, although I've shown just a single
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    piece of wire, actually it starts here, it
    goes around, around, around, around, around,
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    around and then comes out here. So although
    it looks like one piece of wire, it's actually
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    several hundred turns on a coil. And then
    maybe several coils. Simply how it works,
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    we have two things, a magnetic field going
    from north to south represented by these arrows
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    and if I use my left hand, I can say my first
    finger is that direction is the field direction.
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    Now the second thing we have is an electric
    supply going from plus to minus so the electric
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    supply goes up this wire through what is a
    carbon brush, this is a graphite carbon brush
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    into this that we call a commutator. The commutator
    is made of two pieces of copper, this copper
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    disc is connected to this side, this copper
    disc to this side. And these are fixed so
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    as the coil rotates, this rotates. And as
    you can imagine, if this rotates half a turn,
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    the insulating part is going to be against
    the brushes and the electricity will not flow.
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    So what happens when we get a flow of electricity?
    We've got our field. C stand for current,
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    center finger, current, and if I use my left
    hand and put it this way, this is called Flemming's
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    left hand rule and my thumb represents the
    direction of a force which is exerted on the
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    coil. They must be at right angles. So my
    first finger is the field going that way.
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    Now the electric current is coming in here,
    it's going around here and it's going down
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    there. So if I put my center finger in the
    direction of the current, I can see that in
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    fact I will get a force down here and if I
    do the same this side, because this is going
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    this way, the opposite way in fact I'll get
    a force going upwards. So that's my force
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    there. And what will happen is the coil will
    rotate in that direction. If I didn't have
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    this device, it would rotate until it was
    upright and then it would stop and it would
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    stop because as soon as it went over, again
    the force would still be going the same way
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    and it would just hold it upright. So what
    happens is when it reaches the vertical in
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    fact these swap over, the current goes the
    opposite way around and in fact it makes sure
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    that the current in this side of the coil
    that is, even when this side reaches here,
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    the current is always going that way and therefore
    the force is always making it continue to
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    rotate in a circle. Obviously this is going
    to be a very uneven device, it's going to
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    accelerate until it gets vertical, it's going
    to slow down and then it's going to sweep
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    around quickly and slow down again when it's
    vertical. So what normally happens, we have
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    at least three and very often six, nine or
    twelve separate coils, each put at a different
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    angle with separate connections on this side.
    This makes a very smooth electric motor where
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    three or four coils are working at once. So
    this is very simply how an electric motor
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    works.
Title:
Energy & Electricity in Science : How Does an Electric Motor Work?
Duration:
04:31

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