The current in a coil of inductance $0.2 \,H$ changes from $5 \,A$ to $2 \,A$ in $0.5 \,s$. The magnitude of the average induced emf in the coil is (in $\,V$)

The inductance of a coil is $60\,\mu H$. $A$ current in this coil increases from $1.0\,A$ to $1.5\,A$ in $0.1\,s$. The magnitude of the induced $e.m.f.$ is

The total number of turns and cross-section area in a solenoid are fixed. However,its length $L$ is varied by adjusting the separation between windings. The inductance of the solenoid will be proportional to

The $SI$ unit of self-inductance is:

The self-inductance of a long solenoid of cross-sectional area $A$,length $l$ and $n$ turns per unit length is given by

An air-cored solenoid with length $30 \; cm$,area of cross-section $25 \; cm^{2}$ and number of turns $500$,carries a current of $2.5 \; A$. The current is suddenly switched off in a brief time of $10^{-3} \; s$. How much is the average back $emf$ induced (in $V$) across the ends of the open switch in the circuit? Ignore the variation in magnetic field near the ends of the solenoid.