What is the coefficient of mutual inductance when the magnetic flux changes by $2 \times 10^{-2} \, Wb$ and the change in current is $0.01 \, A$?

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 $V$)

$A$ 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

$A$ 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

$A$ solenoid has $2000$ turns wound over a length of $0.3\,m$. The area of cross-section is $1.2\times10^{-3}\,m^2$. Around its central section,a coil of $300$ turns is closely wound. If an initial current of $1\,A$ is reversed in $0.25\,s$,find the emf induced in the coil in $mV$.

Two coils $X$ and $Y$ are placed in a circuit such that when a current changes by $2 \ A$ in coil $X$,the magnetic flux changes by $0.4 \ Wb$ in coil $Y$. The value of mutual inductance of the coils is .... $H$.