Question

A rectangular coil carrying current is placed in a non-uniform magnetic field. On that coil, the total
A. Force is non-zero
B. Force is zero
C. Torque is zero
D. Torque is non-zero

Answer 1

Hint: Electromagnetism is a phenomenon where a magnetic field is created by introducing the current in the conductor; when a conductor is electrically charged, it generates magnetic lines of forces of conductors.
In this question, we need to determine the net force and the net torque acting on the coil carrying current and placed in a non-uniform magnetic field for which we need to use the different properties of the non-magnetic field and the current carrying coil.

Complete step by step answer:
When a current-carrying loop is placed in a magnetic field, it experiences a mechanical force on the coil, which makes the coil to move. This force depends on the length l of the coil, current I through the coil, and the strength of the magnetic field B in which the coil is placed; hence the force will be
\[F = Bil\]
As the magnetic field is non-uniform, the resultant for these forces on different sections will be non-zero.
This mechanical force experienced by the coil due to the non-uniform magnetic field will exert a torque on a loop carrying the current loop, which will spin the coil from its field axis. Given by the formula
\[\tau = F.r.\operatorname{Sin} \theta \], where r is the distance from the pivot that force is applied.
Hence the torque due to the non-uniform magnetic field will also be non-zero.

So, the correct answer is “Option A and B”.

Note:
Students often confuse the terms Uniform and Non-Uniform magnetic fields. A uniform magnetic field is a magnetic field that has the same magnitude and direction throughout the region and has field lines parallel and evenly spaced whereas a non-uniform magnetic field is one in which the field varies in strength and direction at different points, and this can be seen in the field of a bar magnet.