Question

A circular coil expands radially in a region of magnetic field and no electromotive force is produced in the coil. This can be because
A. the magnetic field is constant
B. the magnetic field is in the same plance as the circular coil and it may or may not vary
C. the magnetic field has a perpendicular whose magnitude is decreasing suitably
D. there is a constant magnetic field in the perpendicular (to the plane of the coil) direction

Answer 1

Correct Answer - B::C
When a circular coil expands radially in a region of magnetic field,induced e.m.f. developed is
`e = B xx l xx upsilon = B xx`rateof change of area
Here, magnetic field B is in a plane perpendicular to the plane of cicular coil. As e = 0, magnetic field must be in the plane of circular coil so that is component perpendicular to plane of coil is zero.
Further,if the magnetic field has a component perperdicular to the plane of the coil, whose magnitude is decreasing suitably so that magnetic flux linked with the coil stays constant then `e = (d phi)/(dt) = 0`
Choices (b) and (c ) are correct