Two coaxial coils are very close to each other and their mutual inductance is $5 \,mH$. If a current $i = 50 \sin(500t) \,A$ is passed in one of the coils,then the peak value of the induced e.m.f. in the secondary coil will be ........... $V$.

$A$ circular loop of radius $0.3 \, cm$ lies parallel to a much bigger circular loop of radius $20 \, cm$. The centre of the small loop is on the axis of the bigger loop. The distance between their centres is $15 \, cm$. If a current of $20 \, A$ flows through the smaller loop,then the flux linked with the bigger loop is:

Two planar concentric rings of metal wire having radii $r_1$ and $r_2$ $(r_1 > r_2)$ 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 of self-inductance $25 \ mH$ and $9 \ mH$ are placed close together such that the effective flux in one coil is completely linked with the other. The mutual inductance between these coils is (in $mH$)

If the current $30 \,A$ flowing in the primary coil is made zero in $0.1 \,s$,the $e.m.f.$ induced in the secondary coil is $1.5 \,V$. The mutual inductance between the coils is.....$H$.

Write the formula for the mutual inductance of two very long coaxial solenoids of length $l$.