An induced current of $2 \text{ A}$ flows through a coil. The resistance of the coil is $10 \text{ } \Omega$. What is the change in magnetic flux associated with the coil in $1 \text{ ms}$?

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.

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.

$A$ circular coil of radius $10 \; cm$, $500$ turns, and resistance $2 \; \Omega$ is placed with its plane perpendicular to the horizontal component of the earth's magnetic field. It is rotated about its vertical diameter through $180^{\circ}$ in $0.25 \; s$. The induced e.m.f. in the coil is (Take $B_H = 3.0 \times 10^{-5} \; T$).

$A$ coil has $1,000$ turns and $500 \, cm^2$ as its area. The plane of the coil is placed at right angles to a magnetic induction field of $2 \times 10^{-5} \, Wb/m^2$. The coil is rotated through $180^o$ in $0.2 \, s$. The average $e.m.f.$ induced in the coil,in milli-volts,is

In a circuit with a coil of resistance $2\, \Omega$,the magnetic flux changes from $2.0\, Wb$ to $10.0\, Wb$ in $0.2\, s$. The charge that flows in the coil during this time is..........$C$.