$A$ $10 \; \Omega, 20 \; mH$ coil carrying constant current is connected to a battery of $20 \; V$ through a switch. When the switch is opened, the current becomes zero in $100 \; \mu s$. The average emf induced in the coil is $\dots \; V$.

Regarding self-inductance:
$A:$ The self-inductance of the coil depends on its geometry.
$B:$ Self-inductance does not depend on the permeability of the medium.
$C:$ Self-induced e.m.f. opposes any change in the current in a circuit.
$D:$ Self-inductance is the electromagnetic analogue of mass in mechanics.
$E:$ Work needs to be done against self-induced e.m.f. in establishing the current.
Choose the correct answer from the options given below:

$A$ constant current $I$ is maintained in a solenoid. Which of the following quantities will increase if an iron rod is inserted in the solenoid along its axis?
$(a)$ Magnetic field at the centre
$(b)$ Magnetic flux linked with the solenoid
$(c)$ Self-inductance of the solenoid
$(d)$ Rate of Joule heating

Find out the $e.m.f.$ produced when the current changes from $0$ to $1 \, A$ in $10 \, s$,given $L = 10 \, \mu H$.

When the number of turns in a coil is doubled without any change in the length of the coil,its self-inductance

$A$ coil of wire of radius $r$ has $600$ turns and self-inductance of $108 \ mH$. The self-inductance of a coil with the same radius and $500$ turns is (in $mH$)