00:01
All right, so let's say we have a dipole moment of 3 .8 times 10 to the negative 30th kulum meters.
00:08
And it's in an electric field has a magnitude of 7 times 10 to the 4th newton's per kouom.
00:14
And we want to rotate it from parallel to the field to having a 60 degree angle.
00:20
So we're going to know how much work is done for this.
00:22
So the work is just going to be p .e.
00:24
Times the cosine of theta or times sorry the one minus the cosine of theta and so this is 1 .33 times 10 to the negative 25 jules and we want to know what is the torque on the dipole at that point so this is p .e sine theta so this is going to be about 2 .3 times 10 to the negative 25th newton meters.
00:58
Next question, 43, part a, we have a dipole moment between two charges.
01:04
So we want to calculate what it is.
01:06
So it's going to be q times d, so two nanoculams times the distance between them, which is 0 .04 meters.
01:17
And so this is going to be 8 times 10 to the negative 11th kulum meters.
01:22
And then part b, what's the change in potential energy when it rotates from a line to a field to a 90 degree orientation? the field value is 10 to the 5th newton's per couon.
01:34
So the change in potential energy is going to be basically positive p times e...