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 (n1) times of its maximum value, is:
a. RLln(n−1n)
b. RLln(n−1n+1)
c. RLln(n+1n)
d. RLln(nn−1)