The magnitude of the induced emf in a coil of inductance $30 \ mH$ in which the current changes from $6 \ A$ to $2 \ A$ in $2 \ s$ is: (in $V$)

$A$ coil is wound on a core of rectangular cross-section. If all the linear dimensions of the core are increased by a factor of $3$ and the number of turns per unit length of the coil remains the same,the self-inductance increases by a factor of:

$A$ choke coil works on the principle of

$A$ coil having an inductance of $0.5\, H$ carries a current which is uniformly varying from zero to $10\, A$ in $2\, s$. The $e.m.f.$ (in volts) generated in the coil is

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

$A$ varying current in a coil changes from $10 \,A$ to zero in $1.5 \,s$. If the average emf induced in the coil is $200 \,V$, the self-inductance of the coil is (in $\,H$)