Question

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.

Answer 1

Explanation of Electromagnetic Induction:

1. All magnetic effects are associated with electric current.
2. A moving charge is able to create a magnetic field.
3. The magnetic field produced by a bar magnet can be explained as the resultant field produced by the tiny current loops formed by the electrons revolving around the nucleus of each atom.
4. Hence, any current-carrying wire will produce a magnetic field.
5. The change in the magnetic flux of this magnetic field again induced a current on the conductor.
6. Electromagnetic induction is defined as a phenomenon of the generation of an electrical current by varying the magnetic field in a closed circuit.
7. The electric current produced by this phenomenon is termed an induced current and therefore the voltage set within the circuit because of the induced current is termed induced electromotive force (emf).

Experiment to observe changes in the current due external magnetic field:

1. Take two different coils of copper wire having a huge number of turns (say $50$ and $100$ turns respectively). Insert them over a non-conducting cylindrical roll, as shown within the figure. (You may use a thick paper roll for this purpose.)
2. Connect the coil $1$, having a bigger number of turns, in series with a battery and a plug key. Also, connect the second coil $2$ with a galvanometer as shown.
3. Plugin the key. Observe the galvanometer to test if there's a deflection in its needle. It is observed that the needle of the galvanometer instantly jumps to one side and just as quickly returns to zero, indicating a momentary current in coil $2$.
4. Disconnect coil $1$ from the battery.
5. It is observed that the needle momentarily moves but to the opposite side. It implies that now the current flows in the opposite direction in coil $2$.

Hence, this experiment concludes that a current is set up in a closed-loop system when an external magnetic field passing through the loop increases or decreases.