Question

A wire loop is rotated in a magnetic field. The frequency of change of direction of the induced e.m.f. is -

• A. Four times per revolution
• B. Twice per revolution
• C. Once per revolution
• D. Six times per revolution

Answer 1

The correct option is B Twice per revolution

The magnetic flux associated with the loop is, $\varphi =NBA\cos \omega t$

The induces emf is,
$\left|E\right|=\frac{d\varphi }{dt}=NBA\omega \sin \omega t$

The induced emf becomes zero when,

$\omega t=n\pi$

$\Rightarrow \omega t$ becomes zero at $0,\pi ,2\pi ,3\pi ....$

Hence, the change in direction of induced emf is twice per revolution.

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> Hence, $\left(C\right)$ is the correct answer.