00:01
In this question we are given a square coil of wire that's going to rotate by 90 degrees in a magnetic field and we are going to find the induced emf and the induced current.
00:18
To find that emf, let me grab one color here, so our emf is equal to the negative change in magnetic flux with respect to time.
00:37
And i'm going to go ahead and calculate it with that negative sign and then we'll report the positive value of our answer if it ends up negative.
00:46
So we need the opposite of delta flux and we're going to calculate this flux with our number of turns times the magnetic field times the area of the loop times the cosine of the angle between the normal to the loop and the magnetic field and take all of that divided by our time interval.
01:13
And now here's the thing, n is constant, b is constant, a is constant, so it's going to be the way the cosine of the angle changes as the rotation happens that's going to determine this emf.
01:30
And we're going to have negative nb.
01:35
I called the side length s, so because it's a square, this area will be side length s squared.
01:45
And then we're going to go, well we're going to end at cosine of theta one and we started at cosine of theta not, and we'll talk about what those values are in just a moment.
01:59
And then of course we have our time interval.
02:04
All right, so in the orientation shown in the picture, the normal to the loop is going to either into or out of the page, which means the normal to the loop is parallel to the magnetic field.
02:18
That's an angle of zero degrees...