Two coils have a mutual inductance of $0.005\ \text{H}$. The current changes in the first coil according to equation $I = I_0\sin\omega t$, where $I_0 = 10\ \text{A}$ and $\omega = 60\pi\ \text{rad s}^{-1}$. The maximum values of e.m.f. in the second coil in volt will be

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