What will be the self-inductance of a coil of $100$ turns if a current of $5 \ A$ produces a magnetic flux of $5 \times 10^{-5} \ Wb$?

$A$ solenoid has a length of $1 \,m$ and a cross-sectional area of $0.02 \,m^2$. If the number of turns in the solenoid is $5000$, then the self-inductance of the solenoid is: (in $\pi \,H$)

Current in a circuit falls from $5.0 \, A$ to $0.0 \, A$ in $0.1 \, s$. If an average $emf$ of $200 \, V$ is induced,give an estimate of the self-inductance of the circuit in $Henry$.

The average $e.m.f.$ induced in a coil in which the current changes from $2 \ A$ to $4 \ A$ in $0.05 \ s$ is $8 \ V.$ What is the self-inductance of the coil in $H$?

When the number of turns in a solenoid are doubled without any change in the length of the solenoid,its self-inductance becomes

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