$A$ coil having effective area $A$ is held with its plane normal to a magnetic field of induction $B$. The magnetic induction is quickly reduced to $25 \%$ of its initial value in $1 \ s$. The e.m.f. induced in the coil (in volt) will be

The magnetic flux linked with a coil varies as $\phi = 3t^{2} + 4t + 9$. The magnitude of the emf induced at $t = 2 \text{ s}$ is: (in $\text{ V}$)

$A$ circular loop made of thin copper wire of mass $m$ is placed in a uniform magnetic field such that the plane of the loop is perpendicular to the magnetic field. If $d$ and $\rho$ are the density and resistivity of copper respectively and the magnetic field varies at a constant rate of $\frac{dB}{dt}$,then the induced current in the loop is . . . . . .

$A$ magnet is moved towards a stationary coil with speed $V$. The induced e.m.f. in the coil is $e$. If the magnet and the coil move away from one another,each moving with speed $V$,then the induced e.m.f. in the coil is:

$A$ circular loop of flexible conducting material is kept in a magnetic field directed perpendicularly into its plane. By holding the loop at diametrically opposite points,it is suddenly stretched outwards,then

An electric generator is based on . . . . . .