$A$ coil of wire of a certain radius has $600$ turns and a self-inductance of $108 \, mH$. The self-inductance of a $2^{nd}$ similar coil of $500$ turns will be.........$mH$.

An air-cored solenoid with $30 \ cm$ length,area of cross-section $25 \ cm^2$,and $500$ turns 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 across the ends of the open switch in the circuit (in $V$)? (Ignore the variation in magnetic field near the ends of the solenoid.)

The current passing through a coil of $120$ turns and inductance $40 \text{ mH}$ is $30 \text{ mA}$. The magnetic flux linked with the coil is:

The self-inductance $L$ of a solenoid of length $\lambda$ and area of cross-section $A$ with a fixed number of turns $N$ increases as

The self-inductance of an air-cored solenoid of length $40 \ cm$,diameter $7 \ cm$ having $200$ turns is nearly: (in $\mu H$)

Two different coils have self-inductance $8 \ mH$ and $2 \ mH$. The current in both coils is increased at the same constant rate. The ratio of the induced $emf$s in the coils is