Question

If the switch in the following circuit is turned off, then

• A. The bulb $B_1$ will go out immediately whereas $B_2$ after sometimes
• B. The bulb $B_2$ will go out immediately whereas $B_1$ after sometimes
• C. Both $B_1$ and $B_2$ will go out immediately
• D. Both $B_1$ and $B_2$ will go out after sometime

Answer 1

Answer: (D)

Both $B_1$ and $B_2$ will go out after sometime

When the current is cut off in a $L-R$ circuit, because of induction, current flows for some more time.
When the battery is removed from an $L-R$ circuit, the current decays exponentially. $I\left(t\right)=\frac{ϵ}{R}{e}^{-t/\tau }$ where $\tau =L/R$, the time constant. (In fact the circuit should be closed first and then the battery cut off). Here both the bulbs will go after some time, because the current continues in the circuit for some more time.