Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
A rectangular coil has turns. Each turn is cm by cm. The coil carries A and hangs in a uniform field of T. The plane of the coil makes an angle of with the field. Find the magnetic moment of the coil and the torque on it.
A coil of turns, each of area , has a magnetic moment along its normal. In a field , the torque is , with between the normal and the field. The energy is . An orbiting electron has and .
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. , A, T, and the plane is at to the field.
Step 1. The area. .
Step 2. The moment. .
Step 3. The angle. The normal is at to the plane. So the angle between the normal and the field is .
Step 4. The torque. .
Answer: and .
Watch out. With in place of you would get , which is wrong. A plane that lies along the field gives the greatest torque.
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