A series L-R circuit is connected to a battery of emf V. If the circuit is switched on at t = 0, then the time at which the energy stored in the inductor reaches $\left( {{1 \over n}} \right)$ times of its maximum value, is :

1. A ${L \over R}\ln \left( {{{\sqrt n } \over {\sqrt n + 1}}} \right)$
2. B ${L \over R}\ln \left( {{{\sqrt n } \over {\sqrt n - 1}}} \right)$ Correct answer
3. C ${L \over R}\ln \left( {{{\sqrt n + 1} \over {\sqrt n - 1}}} \right)$
4. D ${L \over R}\ln \left( {{{\sqrt n - 1} \over {\sqrt n }}} \right)$