Question

In the given circuit (fig), the switch is closed at $t=0$. Choose the correct answers :

• A. current in the inductor when the circuit reaches the steady state is 4 A
• B. the net change in flux in the inductor is 1.5 Wb
• C. the time constant of the circuit after closing S is 555.55 s
• D. the change stored in the capacitor in steady state is 1.2 mC

Answer 1

Answer: (A), (B)

the net change in flux in the inductor is 1.5 Wb
current in the inductor when the circuit reaches the steady state is 4 A

When steady state is achieved, all of the current tends to pass through the inductor and it acts as a no resistance wire. Hence current in that part=$\frac{12V}{3\Omega }=4A.$

Flux when S is closed=$LI=0.5\times 4Wb=2Wb$

When S was open, current in the inductor was due to 6 volts battery=$\frac{6V}{3\Omega +3\Omega }=1A$

Flux when S is open$=LI=0.5\times 1=0.5Wb$

Thus change in flux=$1.5Wb$