The current in a coil of inductance $5\, H$ decreases at the rate of $2\, A/s$. The induced $e.m.f.$ is....$V$

What is the self-inductance of a coil in which an induced emf of $2 \,V$ is set up, when the current is changing at the rate of $4 \,A s^{-1}$?

$A$ coil and a bulb are connected in series with a $12 \,V$ direct current $(DC)$ source. $A$ soft iron core is now inserted into the coil. Then,

The momentum in mechanics is expressed as $m \times v$. The analogous expression in electricity is

$A$ 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

$A$ $10 \; \Omega, 20 \; mH$ 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 $\dots \; V$.