Exam Question

5. A coil of inductance 2 H and unknown resistance is connected to a D.C. supply of 100 volts. After 4 ms the current has risen to 75% of its final steady state value. Calculate EACH of the following: (a) the resistance by the coil;(6) (b) the energy stored in the coil when the current has reached its steady state value; (6) (C) the time taken for the current to fall to 50% of its steady state value when the supply is switched off.(4)