A magnetic field is perpendicular to the plane of a flat coil. Since the magnitu

Question

A magnetic field is perpendicular to the plane of a flat coil. Since the magnitude of the field is increasing, an emf will be induced in the coil unless something is done to prevent it. Except for one option, all of the following are possible options that could be used to keep the emf at the zero level. Which option could not be used?




A )Decrease the area of the coil.

B) Increase the angle between the field and the normal to the plane of the coil.

C) Simultaneously decrease the area of the coil and increase the angle between the field and the normal to the plane of the coil.

D) Reduce the time interval during which the magnitude of the field increases

Explanation / Answer

   Induced EMF   E   =   - df / dt                             f   =   B * A * cos ?       a.   decreasing the area of coil such that product of B * A remains same will not make the flux change i.e. no induced emf.    b.   Same effect can be achieved by increasing ? ( that makes cos ? decrease ) such that f remains constant and hence no emf.    c.   It is actually combination of (a) and (b) and can effectively reduce induce emf to zero.   d.    However making dt ( time over which field chages by dB) smaller, will only make e larger. hence this method will not make induced emf zero.

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