00:01
In this problem you're given the circuit and all they want you to do is figure out which of the choices is the proper equation for the right hand loop, what they call loop 3.
00:16
Now, so they've given it to us that it is clockwise.
00:21
They've also indicated the current directions throughout the problem.
00:30
So we'll need that.
00:32
Now remember, when we are going with the current, you're driving potential.
00:38
Current flows to lower potential.
00:42
So we have to watch.
00:44
We're traversing clockwise.
00:48
Are we going with a current when we go through a resistor or against it? so let's start here.
00:54
This is point a that they marked.
00:56
So let's start there.
00:58
We're going through.
00:59
Now the current, i3, is going to be going right to left through i3, i mean through r3 i should say.
01:07
So that means that as you traverse clockwise, left to right, you're going against the current.
01:16
So that's positive.
01:17
You're rising in potential.
01:21
So you would have a term i3, r3.
01:26
Now we get to the battery and we're going to drop minus v3.
01:34
Now we come around to resistor r2.
01:37
The current is going downward.
01:40
We're traversing though upward through it.
01:43
So again, a plus...