A conducing circular loop is placed in a uniform magnetic field of indution `B` tesla with its plane normal to the field. Now, radius of the loop starts shrinking at the rate `(dr//dt)`. Then the induced e.m.f. at the instant when the radius is `r` is:

Options

A. `pirB(dr//dt)`
B. `2pirB(dr//dt)`
C. `pir^(2)(dB//dt)`
D. `(pir^(2)//2)B(dr//dt)`

Answer

B

Explanation

Induced emf, `e=B.(dS)/(dt)=2pirB.(dr)/(dt)`
where, `(dr)/(dt)` is the rate at which radius of loop is shrinking.