Question

A circular coil of 25 turns and radius 12 cm is placed in a uniform magnetic field of 0.5 T normal to the plane of the coil. If the current in the coil is 6 A then total torque acting on the coil is
A. zero
B. 3.4 Nm
C. 3.8 Nm
D. 4.4 Nm

Answer 1

Correct Answer - A
The torque acting on the coil
`|vec(tau)|=|vecm xx vec B|=mB sin theta`
Here the circular coil is placed normal to the direction of magnetic field then the angle between the direction of magnetic moment `(vecm)` and magnetic field `(vecB)` is zero. then
`tau=m B sin theta= m B sin 0=0" "therefore" "tau=0`