Question

The magnetic flux linked with a coil is $\varphi$ and the emf induced in it is $\epsilon$.

• A. If $\varphi =0,\epsilon$ must be 0.
• B. If $\varphi \ne 0,\epsilon$ cannot be 0.
• C. If $\epsilon$ is 0, $\varphi$ may or may not be 0.
• D. None of the above is correct.

Answer 1

The correct option is C If $\epsilon$ is 0, $\varphi$ may or may not be 0.

$ϵ=-\frac{d\varphi }{dt}$
emf depends on the rate of change of flux and not its absolute value.
Therefore if flux is changing and at some instant it is zero, emf will not be zero.
If flux is not zero but at a constant value, then rate of change of flux and therefore emf is zero.
Therefore if emf is zero, flux has to be at a constant zero or nonzero value.