Q. A conducting circular loop is placed in a uniform magnetic field $0.04\ T$ with its plane perpendicular to the magnetic field. The radius of the loop starts shrinking at $2\ mm/s$. The induced $emf$ in the loop when the radius is $2\ cm$ is
A) $3.2\ \pi\mu V$
B) $4.8\ \pi\mu V$
C) $0.8\ \pi\mu V$
D) $1.6\ \pi\mu V$
Explanation
(a) $|e| = \frac{d\phi}{dt} = B\frac{dA}{dt} = B\frac{d}{dt}\left( \pi r^{2} \right) = 2\pi Br\frac{dr}{dt}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.