When a current of $4 \,A$ changes to $8 \,A$ in $0.6 \,s$ in a primary coil, it induces an e.m.f. of $50 \,mV$ in the secondary coil. The mutual inductance between the two coils is: (in $\,mH$)

Two concentric circular coils having radii $r_1$ and $r_2$ $(r_2 \ll r_1)$ are placed co-axially with centres coinciding. The mutual inductance of the arrangement is (Both coils have single turn, $\mu_0$ = permeability of free space)

Two coils $P$ and $S$ have a mutual inductance of $\pi \text{ mH}$. The secondary coil $S$ has resistance $4 \text{ } \Omega$ and self-inductance $(60/\pi) \text{ mH}$. If the current in the primary is $I_p = 12 \sin(50\pi t)$, then the maximum value of the current induced in coil $S$ is [Take $\pi^2 = 10$] (in $\text{ A}$)

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)

There are two coils $A$ and $B$ separated by some distance. If a current of $2 \ A$ flows through $A$,a magnetic flux of $10^{-2} \ Wb$ passes through $B$ (no current through $B$). If no current passes through $A$ and a current of $1 \ A$ passes through $B$,what is the flux through $A$?

In a pair of adjacent coils,if the current in one coil changes from $10 \,A$ to $2 \,A$ in a time $0.2 \,s$,an emf of $120 \,V$ is induced in the other coil. The mutual inductance of the pair of coils is: (in $\,H$)