The area of its cross-section is $1.2 \times {10^{ - 3}}{m^2}$. Around its central section, a coil of $300$ turns is wound. If an initial current of $2A$ in the solenoid is reversed in $0.25\, sec$, then the $e.m.f$. induced in the coil is

Two coils, $X$ and $Y$, are kept in close vicinity of each other. When a varying current, $I(t)$, flows through coil $X$, the induced emf $(V(t))$ in coil $Y$, varies in the manner shown here. The variation of $I(t)$; with time, can then be represented by the graph labelled as graph

$A$ long straight wire is placed along the axis of a circular ring of radius $R$. The mutual inductance of this system is

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 thei 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

There are two long co -axial solenoids of same length $l.$ The inner and outer coils have radii $r_1$ and $r_2$ and number of turns per unit length $n_1$ and $n_2$ respectively. The ratio of mutual inductance to the self -inductance of the inner -coil is

The mutual inductance of a pair of coils, each of $N\,turns$, is $M\,henry$. If a current of $I\, ampere$ in one of the coils is brought to zero in $t$ $second$ , the $emf$ induced per turn in the other coil, in volt, will be