$A$ metallic ring is dropped down, keeping its plane perpendicular to a constant and horizontal magnetic field. The ring enters the region of magnetic field at $t = 0$ and completely emerges out at $t = T \, \text{sec}$. The current in the ring varies as

$A$ circular coil of area $100 \,cm^2$ and $20$ turns is kept in a magnetic field of flux density $2 \,Wb/m^2$. It rotates from a position where its plane makes an angle of $30^{\circ}$ with the field to a position perpendicular to the field in a time $0.2 \,s$. Find the magnitude of the emf induced in the coil due to its rotation. (in $V$)

If a copper ring is moved quickly towards the south pole of a powerful stationary bar magnet,then:

$A$ conducting loop is placed in a uniform magnetic field with its plane perpendicular to the field. An $emf$ is induced in the loop if

$A$ rectangular coil of $100$ turns and size $0.1 \,m \times 0.05 \,m$ is placed perpendicular to a magnetic field of $0.1 \,T$. If the field drops to $0.05 \,T$ in $0.05 \,s$, the magnitude of the e.m.f. induced in the coil is (in $\,V$)

State Lenz's law and prove that it is a specific representation of the law of conservation of energy.