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

Two coils $P$ and $Q$ are separated by some distance. When a current of $3\, A$ flows through coil $P$,a magnetic flux of $10^{-3}\, Wb$ passes through $Q$. No current is passed through $Q$. When no current passes through $P$ and a current of $2\, A$ passes through $Q$,the flux through $P$ is:

If a change in current of $0.01\, A$ in one coil produces a change in magnetic flux of $1.2 \times 10^{-2}\,Wb$ in the other coil,then the mutual inductance of the two coils in henries is.....$H$

$A$ small square loop of wire of side $l$ is placed inside a large square loop of wire of side $L$ $(L \gg l)$. The loops are coplanar and their centers coincide. The mutual inductance of the system is proportional to

The mutual inductance between the rectangular loop and the long straight wire as shown in the figure is $M$.

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