Distinguish between self-induction and mutual induction.

Figure 6.67 shows an inductor L and a resistor R connected in parallel to a battery through a switch. The resistance of R is the same as that of the coil that makes L. Two identical bulbs are put in each arm of the circuit.

Which of the bulbs lights up bright when $S$ is closed?

Give reason for your answer.

Figure 6.67 shows an inductor L and a resistor R connected in parallel to a battery through a switch. The resistance of R is the same as that of the coil that makes L. Two identical bulbs are put in each arm of the circuit.

Will the two bulbs be equally bright after some time?

Give reason for your answer.

A small resistor (say, a lamp) is usually put in parallel to the current-carrying coil of an electromagnet. What purpose does it serve?

How does the self-inductance of an air core coil change, when the number of turns in the coil is decreased?

How does the self-inductance of an air core coil change, when an iron rod is introduced in the coil?

A copper coil $L$ wound on a soft iron core and a lamp $B$ are connected to a battery $E$ through a tapping key $K$. When the key is closed, the lamp glows dimly. But when the key is suddenly opened, the lamp flashes for an instant to much greater brightness. Explain.