When the current in a coil changes from $8 \; A$ to $2 \; A$ in $3 \times 10^{-2} \; s$,the $e.m.f.$ induced in the coil is $2 \; V$. The self-inductance of the coil (in $mH$) is:

$A$ current vs. time graph of the current passing through a solenoid is shown in the figure. For which time is the back electromotive force $(emf)$ a maximum? If the back $emf$ at $t = 3\;s$ is $e$, find the back $emf$ at $t = 7\;s$, $15\;s$, and $40\;s$. $OA$, $AB$, and $BC$ are straight line segments.

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 for a brief time of $10^{-3} \ s$. How much is the (nearly) average back e.m.f. induced across the ends of the open switch in the circuit (in $V$)? (Ignore the variation of magnetic field near the ends of solenoid)

$A$ coil of $100$ turns carries a current of $5\, mA$ and creates a magnetic flux of $10^{-5} \, Wb$. The inductance is.....$mH$.

Two identical inductors carry currents that vary with time according to linear laws (as shown in the figure). In which of the two inductors is the self-induced $emf$ greater?

The current in a coil changes from $2 \,A$ to $5 \,A$ in $0.3 \,s$. The magnitude of emf induced in the coil is $1.0 \,V$. The value of self-inductance of the coil is (in $\,mH$)