Question

the current in a 3H inductor varies at the rate of 3A/s. find the voltage across the inductor and the energy stored in the magnetic field after 2 sec

Answer 1

V = - L di/dt 
    = - 3 H * 3 A /s
    = - 9 Volts

Current at the end of 2 sec = 2 * 3 = 6 A

Energy stored in the magnetic field of the inductor
           = 1/2 L I^2 = 1/2 * 3 * 6² = 54 J