00:01
Here we're going to look at induced current, which means a current circulating in a wire where there is no power supply hooked up to the wire.
00:13
And there are two things that allow us to determine induced current.
00:18
One is faraday's law, which says that you can induce an emf in a wire by having a changing magnetic flux.
00:32
In the circuit in some way.
00:38
And magnetic flux, by the way, is a product of magnetic field normal to the plane loop in its area.
00:50
It's a vector normal to the perimeter of the area.
00:57
The other rule is something called lenses law.
01:01
So there's usually a little negative sign in front of that change.
01:04
Magnetic flux.
01:07
And that negative sign is a philosophical negative.
01:11
It does not mean literally you can always expect a negative voltage.
01:17
What it says is that the emf opposes the change that produced it.
01:31
And i'll just leave off that last phrase.
01:34
But let's take a look at this circuit.
01:36
There is a current being carried through the black wire.
01:41
And if we remember amper's law, that current will produce a magnetic field out of the paper...