Explain Various Experiments performed by Faraday and Henry - Param Himalaya
Experiment 1: Relative motion between a bar magnet and a conducting coil induces electric current in the conducting coil.
Observations : it was observed that:
(i) When the bar magnet was at rest, the galvanometer showed no deflection.
(ii) When the bar magnet with its North pole facing the coil moved towards the coil, the galvanometer showed deflection, indicating flow of current in the coil.
(iii) When the bar magnet with its North pole facing the coil moved away from the coil, the galvanometer again showed the deflection but now in the opposite direction, indicating flow of current in the coil but in the opposite direction.
(iv) The deflection of the galvanometer was large, when the bar magnet was moved faster towards or away from the coil.
(v) When the bar magnet with its South pole facing the coil was brought near the coil, or was moved away from the coil, the galvanometer showed deflection in the opposite direction as compared to that shown with the similar movements of the magnet mentioned in steps (ii) and (iii).
Conclusion:
(i) Whenever there is a relative motion between a closed coil and a magnet, induced e.m.f. is set up across the coil and hence induced current flows through the coil.
(ii) Large induced e.m.f. or current is produced in the coil if the relative motion between the magnet and the coil is large.
(iii) Induced e.m.f. and induced current lasts in the coil so long as the magnet moves w.r.t. the coil.
Experiment 2: Relative motion between a current carrying coil and a conducting coil induces electric current in the conducting coil.
Bar magnet was replaced by a coil of insulated copper wire wound on a wooden core. Coils were not connected physically with one another. One coil was connected to a battery. This coil is called primary coil (P). The second coil placed near the first coil connected to a sensitive galvanometer is called secondary coil (S).
Observations: It was observed that:
(i) the galvanometer connected to the secondary coil showed deflection, when primary coil (P) moved towards it.
(ii) when primary coil (P) moved away from secondary coil (S), the galvanometer in the secondary circuit showed a deflection but in the opposite direction.
(iii) when both primary (P) and secondary (S) coils were stationary, galvanometer showed no deflection.
Explanation: When primary coil moves towards or away from secondary coil, magnetic field or magnetic flux linked with the secondary coil changes which causes the induced e.m.f. or induced current in it till there is relative motion between the coils. Strength of magnetic field improves when iron core is placed in the coil which causes increase in the induced e.m.f.
Conclusion: Induced e.m.f. and thus current is produced in a conducting coil, when there is a relative motion between a current carrying coil and the nearby conducting coil.
Experiment 3: Changing Current in a current carrying coil induces electric current in a nearby coil without relative motion between coils.
In this experiment, coil C1 is connected to a battery through a taping key (TK) and coil C2 is connected to a galvanometer. The axes of both the coils coincide.
Observations:
(i) Galvanometer G shows a momentary deflection, when tapping key TK is pressed. Soon after this, the galvanometer needle returns to zero even if tapping key TK is kept pressed.
(ii) On releasing the key, the galvanometer shows momentary deflection again but in the opposite direction.
(iii) Deflection of the galvanometer increases considerably, when iron bar is inserted in coils.
Explanation: 'On' or 'off' of the current in coil C1 changes the strength of magnetic field produced by it. When the strength of magnetic field linked with coil C1 changes, an e.m.f. is induced in coil C2. Induction stops when change in current i.e., change in magnetic flux in coil C1 and hence in C2 stops. Release of the key brings the current to zero. Decrease in current i.e., decrease in the strength of magnetic field deflects the needle of the galvanometer in the opposite direction.
Conclusion: In this experiment, the coils have no relative motion yet changing current in primary coil induces e.m.f. in the secondary coil and hence electric current flows in the secondary coil.
Conclusion from Faraday's and Henry's experiments:
Induced e.m.f. and induced electric current is produced in a closed circuit by the changing magnetic field through the closed circuit.