Question

A copper disc of radius $0.1 \,m$ is rotated about its centre with $20\, rev/s$ in a uniform magnetic field of $0.1\, T$ with its plane perpendicular to the field. The emf induced across the radius of the disc is:

• A. $\frac{\pi }{20}V$
• B. $\frac{\pi }{10}V$
• C. $20\pi \,mV$
• D. $10\pi \,mV$

Answer 1

Answer: (C)

$20\pi \,mV$

Answer 2

From Faradays law of electromagnetic induction
$e=-\frac{d\phi }{dt}=-BAN.$
Given, $B=0.1\text{ }T,\text{ }N=20,\text{ }A=\pi {{r}^{2}}=\pi {{(0.1)}^{2}}.$ $\therefore$ $e=-0.1\times 20\times \pi {{(0.1)}^{2}}=20\,\pi \,mV$