[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.42,0:00:06.03,Default,,0000,0000,0000,,Hi, I'm Steve Jones and I'm going to explain\Nhow an electric motor works. Now I've drawn
Dialogue: 0,0:00:06.03,0:00:11.25,Default,,0000,0000,0000,,this diagram, it looks rather complicated\Nbut it isn't really that complicated. There
Dialogue: 0,0:00:11.25,0:00:18.25,Default,,0000,0000,0000,,are two main elements. The first is this pair\Nof magnets, one with a north here, the other
Dialogue: 0,0:00:18.52,0:00:24.31,Default,,0000,0000,0000,,with a south here. These are usually permanent\Nmagnets on small motors, but on big motors
Dialogue: 0,0:00:24.31,0:00:31.31,Default,,0000,0000,0000,,they are not. The second main element is this\Ncoil here, although I've shown just a single
Dialogue: 0,0:00:32.53,0:00:37.94,Default,,0000,0000,0000,,piece of wire, actually it starts here, it\Ngoes around, around, around, around, around,
Dialogue: 0,0:00:37.94,0:00:43.29,Default,,0000,0000,0000,,around and then comes out here. So although\Nit looks like one piece of wire, it's actually
Dialogue: 0,0:00:43.29,0:00:50.29,Default,,0000,0000,0000,,several hundred turns on a coil. And then\Nmaybe several coils. Simply how it works,
Dialogue: 0,0:00:51.37,0:00:57.57,Default,,0000,0000,0000,,we have two things, a magnetic field going\Nfrom north to south represented by these arrows
Dialogue: 0,0:00:57.57,0:01:04.57,Default,,0000,0000,0000,,and if I use my left hand, I can say my first\Nfinger is that direction is the field direction.
Dialogue: 0,0:01:08.02,0:01:15.02,Default,,0000,0000,0000,,Now the second thing we have is an electric\Nsupply going from plus to minus so the electric
Dialogue: 0,0:01:16.37,0:01:23.37,Default,,0000,0000,0000,,supply goes up this wire through what is a\Ncarbon brush, this is a graphite carbon brush
Dialogue: 0,0:01:24.37,0:01:31.37,Default,,0000,0000,0000,,into this that we call a commutator. The commutator\Nis made of two pieces of copper, this copper
Dialogue: 0,0:01:33.07,0:01:40.07,Default,,0000,0000,0000,,disc is connected to this side, this copper\Ndisc to this side. And these are fixed so
Dialogue: 0,0:01:40.37,0:01:47.37,Default,,0000,0000,0000,,as the coil rotates, this rotates. And as\Nyou can imagine, if this rotates half a turn,
Dialogue: 0,0:01:48.13,0:01:54.37,Default,,0000,0000,0000,,the insulating part is going to be against\Nthe brushes and the electricity will not flow.
Dialogue: 0,0:01:54.37,0:02:01.37,Default,,0000,0000,0000,,So what happens when we get a flow of electricity?\NWe've got our field. C stand for current,
Dialogue: 0,0:02:01.81,0:02:08.81,Default,,0000,0000,0000,,center finger, current, and if I use my left\Nhand and put it this way, this is called Flemming's
Dialogue: 0,0:02:09.59,0:02:16.59,Default,,0000,0000,0000,,left hand rule and my thumb represents the\Ndirection of a force which is exerted on the
Dialogue: 0,0:02:17.65,0:02:24.65,Default,,0000,0000,0000,,coil. They must be at right angles. So my\Nfirst finger is the field going that way.
Dialogue: 0,0:02:26.66,0:02:33.26,Default,,0000,0000,0000,,Now the electric current is coming in here,\Nit's going around here and it's going down
Dialogue: 0,0:02:33.26,0:02:40.26,Default,,0000,0000,0000,,there. So if I put my center finger in the\Ndirection of the current, I can see that in
Dialogue: 0,0:02:44.93,0:02:51.93,Default,,0000,0000,0000,,fact I will get a force down here and if I\Ndo the same this side, because this is going
Dialogue: 0,0:02:52.78,0:02:59.56,Default,,0000,0000,0000,,this way, the opposite way in fact I'll get\Na force going upwards. So that's my force
Dialogue: 0,0:02:59.56,0:03:06.56,Default,,0000,0000,0000,,there. And what will happen is the coil will\Nrotate in that direction. If I didn't have
Dialogue: 0,0:03:09.63,0:03:16.03,Default,,0000,0000,0000,,this device, it would rotate until it was\Nupright and then it would stop and it would
Dialogue: 0,0:03:16.03,0:03:21.71,Default,,0000,0000,0000,,stop because as soon as it went over, again\Nthe force would still be going the same way
Dialogue: 0,0:03:21.71,0:03:28.71,Default,,0000,0000,0000,,and it would just hold it upright. So what\Nhappens is when it reaches the vertical in
Dialogue: 0,0:03:29.41,0:03:36.00,Default,,0000,0000,0000,,fact these swap over, the current goes the\Nopposite way around and in fact it makes sure
Dialogue: 0,0:03:36.00,0:03:43.00,Default,,0000,0000,0000,,that the current in this side of the coil\Nthat is, even when this side reaches here,
Dialogue: 0,0:03:43.43,0:03:49.50,Default,,0000,0000,0000,,the current is always going that way and therefore\Nthe force is always making it continue to
Dialogue: 0,0:03:49.50,0:03:56.20,Default,,0000,0000,0000,,rotate in a circle. Obviously this is going\Nto be a very uneven device, it's going to
Dialogue: 0,0:03:56.20,0:04:00.34,Default,,0000,0000,0000,,accelerate until it gets vertical, it's going\Nto slow down and then it's going to sweep
Dialogue: 0,0:04:00.34,0:04:05.77,Default,,0000,0000,0000,,around quickly and slow down again when it's\Nvertical. So what normally happens, we have
Dialogue: 0,0:04:05.77,0:04:12.77,Default,,0000,0000,0000,,at least three and very often six, nine or\Ntwelve separate coils, each put at a different
Dialogue: 0,0:04:15.53,0:04:22.53,Default,,0000,0000,0000,,angle with separate connections on this side.\NThis makes a very smooth electric motor where
Dialogue: 0,0:04:22.82,0:04:29.26,Default,,0000,0000,0000,,three or four coils are working at once. So\Nthis is very simply how an electric motor
Dialogue: 0,0:04:29.26,0:04:29.70,Default,,0000,0000,0000,,works.