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

Answer

D

Explanation

Induced emf
`= epsilon = (d phi)/(d t) = (d(B.A))/(d t)`