Question

In the figure, the switch $S$ is closed so that a current flows in the iron-core inductor which has inductance $L$ and the resistance $R$. When the switch is opened, a spark is obtained in it at the contacts. The spark is due to

• A. a slow flux change in $L$
• B. a sudden increase in the emf of the battery $B$
• C. a rapid flux change in $L$
• D. a rapid flux change in $R$

Answer 1

The correct option is C a rapid flux change in $L$

When switch $S$ is closed, we see that the current flows through the circuit and there will be energy stored in the inductor. When switch $S$ is opened, the voltage drop across the resistance will instantly come to zero, but in the inductor, there will be some energy and due to that a rapid flux change occurs in $L$.
$\because \varphi =LI$