Explain briefly different methods of producing induced electromotive force $(emf)$.

(N/A) $(i)$ By changing the magnetic flux linked with a coil,an $emf$ can be induced. This can be achieved by varying the current in a neighboring coil (mutual induction).
$(ii)$ By moving a magnet towards or away from a stationary coil,the magnetic field lines passing through the coil change,thereby inducing an $emf$ (electromagnetic induction).
$(iii)$ By rotating a coil within a uniform magnetic field,the angle between the area vector and the magnetic field changes,resulting in a change in magnetic flux and the induction of an $emf$.