Question
A current carrying coil of 200 turns has an area of cross-section 1 x 10–4 m2. When suspended freely through its centre, it can turn in a horizontal plane. What is the magnetic moment of the coil for a current of 5 A? Also calculate the net force and torque on coil if a uniform horizontal field of 10 x 10–2 T is set up at an angle of 30° with axis of coil when it is carrying the same current.
Solution
Here,
Number of turns, N = 200
Area of cross-section. A = 1 x 10–4 m2
Current passing through the coil, I = 5 A
M =?
Magnetic momemnt of the coil, M = N IA
= 200 x 5 x 10–1
= 10–1 JT–1
In a uniform horizontal field B = 10 x 10–2 T, the ends of coil experience equal and opposite forces. Therefore, net force on the coil = 0.
Therefore, torque acting on the coil is,