A small square loop of wire of side $l$ is placed inside a large square loop of wire $L(L \gg l)$. Both loops are coplanar and their centres coincide at point $O$ as shown in figure. The mutual inductance of the system is.
$\frac{2 \sqrt{2} \mu_{0} L ^{2}}{\pi \ell}$
$\frac{\mu_{0} \ell^{2}}{2 \sqrt{2 \pi L}}$
$\frac{2 \sqrt{2} \mu_{0} \ell^{2}}{\pi L }$
$\frac{\mu_{0} L ^{2}}{2 \sqrt{2} \pi \ell}$
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
A short solenoid (length $l$ and radius $r$ with $n$ turns per unit length) lies well inside and on the axis of a very long, coaxial solenoid (length $L$, radius $R$ and $N$ turns per unit length, with $R>r$ ). Current $I$ follows in the short solenoid. Choose the correct statement.
A coil of radius $1\, cm$ and of turns $100$ is placed in the middle of a long solenoid of radius $5\, cm$. and having $5\, turns/cm$. parallel to the axis of solenoid The mutual inductance in millihenery will be
Mutual inductance of two coils can be increased by
Two coils have mutual inductance $0.002 \ \mathrm{H}$. The current changes in the first coil according to the relation $\mathrm{i}=\mathrm{i}_0 \sin \omega \mathrm{t}$, where $\mathrm{i}_0=5 \mathrm{~A}$ and $\omega=50 \pi$ $\mathrm{rad} / \mathrm{s}$. The maximum value of $\mathrm{emf}$ in the second coil is $\frac{\pi}{\alpha} \mathrm{V}$. The value of $\alpha$ is_______.