The magnitude of flux linked with a coil varies with time as $\phi = 3t^2 + 4t + 7$. The magnitude of the induced e.m.f. at $t = 2 \ s$ is: (in $V$)

Two identical circular coils $A$ and $B$ are kept on a horizontal tube side by side without touching each other. If the current in the coil $A$ increases with time,in response,the coil $B$

Assertion : Lenz's law violates the principle of conservation of energy.
Reason : Induced $emf$ always opposes the change in magnetic flux responsible for its production.

$A$ coil has $200$ turns and an area of $70 \ cm^2$. The magnetic field perpendicular to the plane of the coil is $0.3 \ Wb/m^2$ and it takes $0.1 \ s$ to rotate through $180^o$. The value of the induced $e.m.f.$ will be ...... $V$.

Lenz's law is expressed by the following formula (here $e$ = induced $e.m.f.$,$\phi$ = magnetic flux in one turn and $N$ = number of turns).

$A$ square loop of side $10 \; cm$ and resistance $0.5 \; \Omega$ is placed vertically in the east-west plane. $A$ uniform magnetic field of $0.10 \; T$ is set up across the plane in the north-east direction. The magnetic field is decreased to zero in $0.70 \; s$ at a steady rate. Determine the magnitudes of induced emf and current during this time interval.