Question

A coil of inductance 10 H, resistance 40 Ω is connected as shown in the figure. The switch S connected with point 1 for a very long time, is moved to point 2 at t=0. If, at t=0^+, the voltage across the coil is 120 V, the value of the resistance R is __________

(a) Zero

(b) 20 Ω

(c) 40 Ω

(d) 60 Ω

I got this question in exam.

I'm obligated to ask this question of Calculation of I(0+), di/dt(0+), d2I/dt2(0+) in Circuits Involving both Capacitor and Inductor topic in portion Application of the Laplace Transform in Circuit Analysis of Network Theory

Answer 1

The correct answer is (a) Zero

Explanation: IL at 0^– = \(\frac{120}{60}\) = 2A

120 = 2(R + 40 + 20)

∴ R = 0.