00:02
Okay, we're going to do problem number 13.
00:07
All right.
00:09
So let's get that set up here.
00:13
All right, we're going to start with the equation v for velocity equals e, elementary charge, times b, the magnetic field, times the radius.
00:25
And it's all going to be over the mass.
00:28
Now, if we rearrange this and solve this, or move mass over, because we don't want to keep it as a fraction.
00:34
So we'll do this.
00:37
All right.
00:43
Now remember, momentum is also equal to mv.
00:50
So what we'll do is we'll take this and we'll put it right in there for the velocity times mass.
00:58
All right.
00:58
So it'll now look like this.
01:02
Momentum is equal to elementary charge times b times r.
01:09
It's like that.
01:10
Now, if you also recall, i'm going to go back over here in this side.
01:17
Momentum in a relativistic sense is also equal to energy over speed of light.
01:25
So we can do a little substitution.
01:28
We can take this right here and we'll substitute this in.
01:33
If we do that, we should get e over c equal to elementary charge b times r.
01:45
Now, it's asking for the ratio of the energy to the elementary charge, like such.
01:50
So what we're going to do is we're going to multiply each side by c...