Question

If the instantaneous magnetic flux and induced emf produced in a coil is $\varphi$ and $E$ respectively, then according to Faraday's law of electro magnetic induction:

• A. $E$ must be zero if $\varphi =0$ and changing
• B. $E\ne 0$ if $\varphi =0$
• C. $E\ne 0$ if $\varphi$ is changing.
• D. $E=0$ then $\varphi$ must be zero

Answer 1

Answer: (C)

$E\ne 0$ if $\varphi$ is changing.

Farady's law states that time varying magnetic flux can induce an e.m.f.
E = Electric field, Induced
$E=-\frac{d\varphi }{dt}$
$E=-\frac{d\varphi }{dt}$
$E=0$ only if $\frac{d\varphi }{dt}=0$
If $E=0$, then $\varphi =const.$
$E\ne 0$, then $\varphi$ is changing