Question

A circular ring is expanding in a uniform magnetic field of 2 T, which is perpendicular to the plane of the ring such that, its radius is increasing at a rate of 2 cm/s. Induced EMF in the ring when radius is 40 cm is

• A. $32\pi mV$
• B. $60\pi mV$
• C. $12mV$
• D. $15mV$

Answer 1

The correct option is A $32\pi mV$

$|E|=\frac{d\varphi }{dt}=\frac{d}{dt}BA=\frac{d}{dt}B\pi r^2=2B\pi r\frac{dr}{dt}$
$E=2\times 2\times \pi \times \frac{40}{100}\times 2\times {10}^{-2}=32\pi mV$