Two conducting circular loops $A$ and $B$ are placed in the same plane with their centres coinciding as shown in the figure. If $b >> a$,the mutual inductance between them is:

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 $mWb$)

The coefficient of mutual inductance between the primary and the secondary coil of a transformer is $0.2 H$. When the current in the primary coil changes at a rate of $5 A s^{-1}$,the induced emf in the secondary coil will be: (in $V$)

$A$ 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 $(\mu_0 = \text{permeability of free space})$

$X$ and $Y$ are two circuits having a coefficient of mutual inductance $3 \text{ mH}$ and resistances $10 \text{ } \Omega$ and $4 \text{ } \Omega$ respectively. To have an induced current of $60 \times 10^{-4} \text{ A}$ in circuit $Y$,the amount of current to be changed in circuit $X$ in $0.02 \text{ s}$ is: (in $A$)

The mutual inductance between a primary and secondary circuit is $0.5 \, H$. The resistances of the primary and the secondary circuits are $20 \, \Omega$ and $5 \, \Omega$ respectively. To generate a current of $0.4 \, A$ in the secondary,the current in the primary must be changed at the rate of . . . . . . $A/s$.