A coil of wire of radius ' $r$ ' has 600 turns and a self-inductance of 108 mH . The self-inductance of a coil with same radius and 500 turns is

A coil of ' $n$ ' turns and resistance $R \Omega$ is connected in series with a resistance $\frac{R}{2}$. The combination is moved for time ' $t$ ' second through magnetic flux $\phi_1$ to $\phi_2$. The induced current in the circuit is

The equivalent inductance between A and B is equal to

A coil of ' $n$ ' turns and area ' $A$ ' is suddenly removed from a magnetic field, a charge ' $q$ ' flows through the coil. If resistance of the coil is ' $R$ ' then the magnetic flux density is (in $\mathrm{Wb} / \mathrm{m}^2$ )