A 12v battery connected to a $6 \Omega$, 10H coil through a switch drives a constant current in the circuit. Th switch is suddenly opened. Assuming that it took 1 millisecond to open the switch. Calculate the average e.m.f induced across the coil.

Question

(a) $2 \times 10^{-4} V$
(b) $2 \times 10^4 V$
(c) $0.2 \times 10^{-4} V$
(d) $0.2 \times 10^4 V$