Question

A circular loop of radius $r$, having $N$ turns of a wire, is placed in a uniform and constant magnetic field $B$. The normal loop makes an angle $\theta$ with the magnetic field. Its normal rotates with an angular velocity $\omega$ such that the angle $\theta$ is constant. Choose the correct statement from the following.

• A. emf in the loop is $NB\omega r^2/2\cos \theta$
• B. emf induced in the loop is zero
• C. emf must be induced as the loop crosses magnetic lines.
• D. emf must not be induced as flux does not change with time.
• E. answer required

Answer 1

Answer: (B), (D)

emf induced in the loop is zero
emf must not be induced as flux does not change with time.

Clearly since the angle of the normal remains costant, the wheel rotates in its plane.
THe magnetic flux through it does not change with time on rotation,
hence by faraday' law, no EMF is induced.
(NOTE: the answer would be different in case of a disc)