$A$ coil of radius $r$ is placed on another coil (whose radius is $R$ and current flowing through it is changing) so that their centres coincide. $(R \gg r)$ If both the coils are coplanar,then the mutual inductance between them is proportional to

The mutual inductance between two coils is $1.25 \ H$. If the current in the primary coil changes at the rate of $80 \ A/s$, then the induced $e.m.f.$ in the secondary coil is ...... $V$.

Two coils of self-inductance $2 \, mH$ and $8 \, mH$ are placed so close together that the effective flux in one coil is completely linked with the other. The mutual inductance between these coils is......$ mH$

$A$ small square loop of side $a$ and one turn is placed inside a larger square loop of side $b$ and one turn $(b \gg a)$. The two loops are coplanar with their centres coinciding. If a current $I$ is passed in the square loop of side $b$,then the coefficient of mutual inductance between the two loops is

The inductors of two $LR$ circuits are placed next to each other,as shown in the figure. The values of the self-inductance of the inductors,resistances,mutual-inductance,and applied voltages are specified in the given circuit. After both the switches are closed simultaneously,the total work done by the batteries against the induced $EMF$ in the inductors by the time the currents reach their steady-state values is . . . . $mJ$.

Two coils $P$ and $Q$ are kept near each other. When no current flows through coil $P$ and current increases in coil $Q$ at the rate of $10 \ A/s$,the e.m.f. in coil $P$ is $15 \ mV$. When coil $Q$ carries no current and current of $1.8 \ A$ flows through coil $P$,the magnetic flux linked with coil $Q$ is (in $mWb$)