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 :

Options

A. `pi/20V`
B. `pi/10V`
C. `20pimV`
D. `10pimV`

Answer

C

Explanation

From Faraday.s law of electromagnetic induction
`" "e=(dphi)/(dt)=-BAN`.
Given, `B=0.1, N=20, A=pir^(2)=pi(0.1)^(2)`.
`therefore" "e=0.1 times 20 times pi(0.1)^(2)=20pi" "mV`