Question

Determine the voltage across the inductor in the circuit shown below is?

(a) VL = 60(-e^-2t)V

(b) VL = 60(e^2t)V

(c) VL = 60(e^-2t)V

(d) VL = 60(-e^2t)V

I have been asked this question in unit test.

This intriguing question comes from DC Response of an R-L Circuit topic in section Transients of Network Theory

Answer 1

The correct answer is (c) VL = 60(e^-2t)V

Easy explanation: Voltage across the inductor VL = Ldi/dt. On substituting the expression of current we get voltage across the inductor = 15×(d/dt)(2(1-e^-2t)))=60(e^-2t)V.