Two coils are placed close to each other. The mutual inductance of the pair of coils depends upon

Two circular coils can be arranged in any of the three situations shown in the figure. Their mutual inductance will be:

Two coaxial solenoids are made by winding thin insulated wire over a pipe of cross-sectional area $A=10 {\mathrm{cm}}^2$ and length $=20 \mathrm{cm}.$ If one of the solenoids has $300$ turns and the other $400$ turns, their mutual inductance is

$\left({\mu }_0=4\pi \times {10}^{-7} T m A^{-1}\right):$

The radius of the circular conducting loop shown in the figure is $R$. The magnetic field is decreasing at a constant rate $\alpha$. Resistance per unit length of the loop is $\rho$. Then current in the wire $AB$ is ($AB$ is one of the diameters)