The magnetic potential energy stored in a certain inductor is $49\ \text{mJ}$ when the current in the inductor is $70\ \text{mA}$. The inductance of the inductor is

Two planar concentric rings of metal wire having radii '$r_1$' and '$r_2$' (with $r_1 > r_2$) are placed in air. The current 'I' is flowing through the coil of larger radius. The mutual inductance between the coils is given by ( $\mu_0$ = permeability of free space)

Two coils having self-inductance $L_1 = 75$ mH and $L_2 = 48$ mH are coupled with each other. If the mutual inductance of the coils is 37.2 mH, then coefficient of coupling will be

A straight line conductor of length 0.4 m is moved with a speed of $7.0 \text{ ms}^{-1}$ perpendicular to magnetic field of intensity $0.8 \text{ Wb m}^{-2}$. The induced e.m.f. across the conductor is