A circular coil expands radially in a region of magnetic field and no electromotive force is produced in the coil. This can be because

Options

A. the magnetic field is constant.
B. the magnetic field is in the same plane as the circular coil and it may or may not vary
C. the magnetic field has a perpendicular (to the plane of the coil) component whose magnitude is decreasing suitably.
D. there is a constant magnetic field in the perpendicular (to the plane of the coil) direction.

Answer

B, C

Explanation

When a circular coil expands in a magnetic field and the magnetic field is in the plane of coil, so no magnetic flux will link with the coil and induced emf e = 0 and magnetic field perpendicular to the plane of coil decreases suitably and the magnetic flux linked with coil remains constant hence induced emf e = 0.