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

$A$ long coaxial cable carries current $I$ along its surface. The current flows down the surface of the inner cylinder of radius $a$ and back along the outer cylinder of radius $b$.

$A$ coil is wound on a core of rectangular cross-section. If all the linear dimensions of the core are increased by a factor of $2$ and the number of turns per unit length of the coil remains the same, the self-inductance increases by a factor of (Assume, permeability is same).

The equivalent quantity of mass in electricity is

Write down the formula for the self-inductance of a very long solenoid.

The self-inductance of a coil depends on