Explain the phenomenon of electromagnetic induction. Describe an experiment to show that a current is set up in a closed loop when an external magnetic field passing through the loop increases or decreases.

(N/A) Electromagnetic induction is the phenomenon where a changing magnetic field in a conductor induces an electric current in another conductor or circuit.
Experiment:
$1$. Take two coils of copper wire having a large number of turns (say $50$ and $100$ turns respectively) and wind them over a non-conducting cylindrical roll.
$2$. Connect the terminals of the first coil (Coil-$1$) in series with a battery and a plug key $(K)$.
$3$. Connect the terminals of the second coil (Coil-$2$) to a galvanometer $(G)$.
$4$. When the key $K$ is closed,a current flows through Coil-$1$,creating a magnetic field. The galvanometer needle in Coil-$2$ shows a momentary deflection,indicating that a current is induced in Coil-$2$.
$5$. When the key $K$ is opened,the current in Coil-$1$ stops,causing the magnetic field to change. The galvanometer needle deflects in the opposite direction,indicating an induced current in the opposite direction.
$6$. This experiment demonstrates that a change in the magnetic field associated with a coil induces a current in it.