When the current changes from + 2 A to - 2A in 0.05 s, an emf of 8 V is induced in a coil. The coefficient of self-induction of the coil is :
0.2 H
0.4 H
0.8 H
0.1 H
e=-L∆i∆t⇒L=e-∆i/∆t