In a fluorescent lamp choke (a small transformer),$100 \; V$ of reverse voltage is produced when the choke current changes uniformly from $0.25 \; A$ to $0 \; A$ in a duration of $0.025 \; ms$. The self-inductance of the choke (in $mH$) is estimated to be:

$A$ solenoid is connected to a battery so that a steady current flows through it. If an iron core is inserted into the solenoid,the current will

The current in self-inductance $L=40\; mH$ is to be increased uniformly from $1\; A$ to $11\; A$ in $4\; ms$. The $e.m.f.$ induced in the inductor during this process is ..... $V$.

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.

The length of thin wire required to manufacture a solenoid of inductance $L$ and length $\ell$ (if cross-sectional diameter is considered much less than its length) is:

When a current in the conducting coil is changed from $5 \ A$ in one direction to $5 \ A$ in the opposite direction in $0.5 \ s$,an average induced e.m.f. in the coil is $2 \ V$. The self-inductance of the coil is (in $mH$)