Two solenoids of equal number of turns have their lengths as well as radii in the same ratio $1: 3$. The ratio of their self-inductance will be

What is the self-inductance of a coil which produces a self-induced $EMF$ of $5 \ V$ when the current changes from $3 \ A$ to $2 \ A$ in $1 \ ms$?

The unit of self-inductance of a coil is

The self-inductance of a straight conductor is

$A$ coil of wire of radius $r$ has $600$ turns and self-inductance of $108 \ mH$. The self-inductance of a coil with the same radius and $500$ turns is (in $mH$)

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)