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Hi, I'm Steve Jones and I'm going to explain[br]how an electric motor works. Now I've drawn

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this diagram, it looks rather complicated[br]but it isn't really that complicated. There

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are two main elements. The first is this pair[br]of magnets, one with a north here, the other

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with a south here. These are usually permanent[br]magnets on small motors, but on big motors

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they are not. The second main element is this[br]coil here, although I've shown just a single

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piece of wire, actually it starts here, it[br]goes around, around, around, around, around,

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around and then comes out here. So although[br]it looks like one piece of wire, it's actually

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several hundred turns on a coil. And then[br]maybe several coils. Simply how it works,

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we have two things, a magnetic field going[br]from north to south represented by these arrows

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and if I use my left hand, I can say my first[br]finger is that direction is the field direction.

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Now the second thing we have is an electric[br]supply going from plus to minus so the electric

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supply goes up this wire through what is a[br]carbon brush, this is a graphite carbon brush

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into this that we call a commutator. The commutator[br]is made of two pieces of copper, this copper

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disc is connected to this side, this copper[br]disc to this side. And these are fixed so

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as the coil rotates, this rotates. And as[br]you can imagine, if this rotates half a turn,

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the insulating part is going to be against[br]the brushes and the electricity will not flow.

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So what happens when we get a flow of electricity?[br]We've got our field. C stand for current,

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center finger, current, and if I use my left[br]hand and put it this way, this is called Flemming's

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left hand rule and my thumb represents the[br]direction of a force which is exerted on the

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coil. They must be at right angles. So my[br]first finger is the field going that way.

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Now the electric current is coming in here,[br]it's going around here and it's going down

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there. So if I put my center finger in the[br]direction of the current, I can see that in

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fact I will get a force down here and if I[br]do the same this side, because this is going

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this way, the opposite way in fact I'll get[br]a force going upwards. So that's my force

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there. And what will happen is the coil will[br]rotate in that direction. If I didn't have

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this device, it would rotate until it was[br]upright and then it would stop and it would

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stop because as soon as it went over, again[br]the force would still be going the same way

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and it would just hold it upright. So what[br]happens is when it reaches the vertical in

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fact these swap over, the current goes the[br]opposite way around and in fact it makes sure

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that the current in this side of the coil[br]that is, even when this side reaches here,

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the current is always going that way and therefore[br]the force is always making it continue to

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rotate in a circle. Obviously this is going[br]to be a very uneven device, it's going to

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accelerate until it gets vertical, it's going[br]to slow down and then it's going to sweep

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around quickly and slow down again when it's[br]vertical. So what normally happens, we have

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at least three and very often six, nine or[br]twelve separate coils, each put at a different

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angle with separate connections on this side.[br]This makes a very smooth electric motor where

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three or four coils are working at once. So[br]this is very simply how an electric motor

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works.