If a coil of $40$ turns and area $4 \, cm^2$ is suddenly removed from a magnetic field,it is observed that a charge of $2 \times 10^{-4} \, C$ flows through the coil. If the resistance of the coil is $80 \, \Omega$,the magnetic flux density in $Wb \, m^{-2}$ is:

The magnitude of induced emf is directly proportional to the rate of change of magnetic flux linked with the coil. This statement is known as

It is desired to measure the magnitude of the magnetic field between the poles of a powerful loudspeaker magnet. $A$ small flat search coil of area $2 \; cm^{2}$ with $25$ closely wound turns is positioned normal to the field direction and then quickly snatched out of the field region. (Equivalently,one can give it a quick $90^{\circ}$ turn to bring its plane parallel to the field direction). The total charge flown in the coil (measured by a ballistic galvanometer connected to the coil) is $7.5 \; mC$. The combined resistance of the coil and the galvanometer is $0.50 \; \Omega$. Estimate the field strength of the magnet.

The coil of a dynamo is rotating in a magnetic field. The developed induced $e.m.f.$ changes and the number of magnetic lines of force also changes. Which of the following conditions is correct?

Assertion : Faraday's laws are consequences of conservation of energy.
Reason : In a purely resistive $A.C.$ circuit,the current lags behind the $e.m.f.$ in phase.

Two identical metallic square loops $L_1$ and $L_2$ are placed next to each other with their sides parallel on a smooth horizontal table. Loop $L_1$ is fixed and a current which increases as a function of time is passed through it. Then,loop $L_2$ is