The current in a coil of inductance `5H` decreases at the rate of `2A//a`. The induced e.m.f. is

A current through a choke coil of self inductance 2H decreases at the rate of 0.5A//s . The e.m.f. developed across the coil is

The current passing through a choke coil of 5H is decreasing at the rate of 2A/s. The e.m.f. developed across the coil is?