Question

When a wire loop is rotated in a magnetic field, the direction of induced e.m.f. changes once in each

• A. $1/4$ revolution
• B. $1/2$ revolution
• C. $1$ revolution
• D. $2$ revolution

Answer 1

The correct option is B $1/2$ revolution

Flux of the magnetic field through the loop

$\varphi =B.A\cos \omega t$

Emf= $-\frac{d\varphi }{dt}=B.A\omega \sin \omega t$

$\omega t=0to\pi ,\sin \omega t=+ve$

$\omega t=\pi to2\pi ,\sin \omega t=-ve$

Hence, the direction of induced e.m.f. changes once in $\frac{1}{2}$ revolution.