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# A circular coil of area $0.04 m^2$, 200 turns and resistance 2 $\Omega$ changes from $0.1 \;Wb \;m^{−2}$ to $0.04 \;Wb\; m^{−2}$ in $0.02 \text{seconds}$. Find the induced emf.

1. (A) 24V

(B) 12V

(C) 6V

(D) 36V

Given $N = 200$, $A = 0.04m^2$, $B_1 = 0.1 \;Wb \;m^{−2}$,  $B_2 = 0.04 \;Wb\; m^{-2}$ <p></p>

Induced emf $\varepsilon = -\large\frac{d\Phi}{dt} = -\large\frac{d NBA }{dt} =$$-NA$$\large\frac{B_2-B_1}{dt}$ <p></p>

$\varepsilon = -200 \times \ 0.04 m^2 \times \large\frac{0.04-0.1}{0.02}$$= 24V$