Find the mutual inductance between two coaxial circular loops of radius $a$ separated by a distance $l$,where $l >> a$.

Two coils $A$ and $B$ are wound on the same iron core as shown in the figure. The number of turns in the coils $A$ and $B$ are $N_A$ and $N_B$ respectively. Identify the correct statement.

There are $10$ turns in coil $M$ and $15$ turns in coil $N$. If a current of $2\ A$ is passed through coil $M$,then the flux linked with coil $N$ is $1.8 \times 10^{-3}\ Wb$. If a current of $3\ A$ is passed through coil $N$,then the flux linked with coil $M$ is:

$A$ transformer works on the principle of

$A$ solenoid of length $60 \ cm$ with $15$ turns per $cm$ and area of cross-section $4 \times 10^{-3} \ m^2$ completely surrounds another co-axial solenoid of the same length and area of cross-section $2 \times 10^{-3} \ m^2$ with $40$ turns per $cm$. The mutual inductance of the system is: (in $mH$)

There are two long coaxial solenoids of the same length $l$. The inner and outer coils have radii $r_1$ and $r_2$ and number of turns per unit length $n_1$ and $n_2$ respectively. The ratio of mutual inductance to the self-inductance of the inner coil is