Question

In the circuit shown below, the switch is closed at t = 0, applied voltage is v (t) = 100cos (103t+π/2), resistance R = 20Ω and inductance L = 0.1H. The value of c in the complementary function of ‘i’ is?

(a) c = -0.98cos⁡(π/2-78.6^o)

(b) c = -0.98cos⁡(π/2+78.6^o)

(c) c = 0.98cos⁡(π/2+78.6^o)

(d) c = 0.98cos⁡(π/2-78.6^o)

I had been asked this question in an interview for job.

Enquiry is from Sinusoidal Response of an R-L Circuit topic in division Transients of Network Theory

Answer 1

Right option is (a) c = -0.98cos⁡(π/2-78.6^o)

To explain: At t = 0, the current flowing through the circuit is zero. Placing i = 0 in the current equation we get c = -0.98cos⁡(π/2-78.6^o).