Christian Ø rsted discovered that magnetic fields are produced by the electrical current. Electromagnetic induction was observed separately by Michael Faraday in 1831 and Joseph Henry in 1832. However, Michael Faraday was the first to publish the results of his experiments and hence the induction laws are called Faraday’s laws.

Faraday’s law indicates how electromotive force (EMF) is generated when a magnetic field interacts with an electric current. The phenomenon through which the EMF is produced is called electromagnetic induction. It is the basic underlying principle by which many electrical motors, inductors, generators, transformers and solenoids operate. Michael Faraday postulated two electromagnetic induction laws. The first of Faraday’s laws explains how an EMF is induced in a conductor when it is kept in a changing magnetic field, while the second Faraday’s law determines the strength of the EMF produced in the conductor. 

How does Faraday’s law work?

Michael Faraday devised three experiments to explain his theory of electromagnetic induction and to formulate Faraday’s laws.

Experiment 1

• Consider a coil A which is linked to a galvanometer. 
• The pointer in the galvanometer shows a deflection when the north pole of a bar magnet is brought near the coil. This shows that there is an electric current in the coil.  The deflection only occurs while the magnet is moving and there is no deflection when the magnet is not moving. This shows that a current is induced due to the variation of the magnetic field as proposed by the first Faraday’s law.
• The galvanometer indicates a deflection in the opposite direction when the magnet is taken away from the coil. This shows that the direction of the current in the coil has been reversed. 
• It is also observed that the deflections of the galvanometer when the south pole of the bar magnet is brought near or taken away from the coil are opposite to that seen when the north pole is brought near or taken away. 
• The galvanometer shows a larger deflection which means that there is a higher current, when the magnet is brought near or moved away from the coil at a faster rate.
• The same deflections are observed when the coil is taken near or moved away from a fixed bar magnet. 

This establishes that the induction of electric current in the coil is due to the relative motion between the coil and the magnet which is in line with Faraday’s law.

Experiment 2

• In this experiment consider that the magnet is replaced by a second coil B connected to an electric battery and the coil A is still connected to the galvanometer. A stable magnetic field is produced by the steady current in the coil B. 
• The galvanometer indicates a deflection as the coil B is taken near coil A. This shows that there is an induced electric current in coil A. 
• The galvanometer shows a deflection in the opposite direction when the coil B is taken away from coil A. 
• The deflection of the galvanometer in both cases is present only while the coil B is moving and disappears when the coil B is not moving. 
• The same deflections are observed when coil A is moved while coil B remains stationary.
• This again establishes that the induced electric current is due to the relative motion between the coil which is in line with Faraday’s law.

Experiment 3

• The first two showed that relative motion between a magnet and a coil or between two coils generated an electric current. This experiment confirms that relative motion is not essential for the induction of electric current. 
• Consider two stationary coils A and B. Coil A is linked to a galvanometer while the Coil B is linked to a battery through a tapping key. 
• The galvanometer reads a short deflection when the key is pressed and returns to zero immediately.
• There is no deflection in the galvanometer when the key is continuously pressed. However, a deflection in the opposite direction is seen when the key is released.
• This indicates that a current is induced in coil A when there is a change in the current of the coil B.
• Another experiment shows that a massive deflection is observed when an iron rod which has magnetic properties is introduced along the axis of the coils. This shows that a change in the magnetic field produces an induced current in line with Faraday’s law.

Does an AC generator work on Faraday’s law?

• Electromagnetic induction has led to many technological advancements. A vital use of electromagnetic induction is in the generation of alternating currents (AC). 
• Electromotive force or a current can be induced in a coil by rotating it or changing its effective area. The effective area of the coil changes as the coil rotates in a magnetic field.  This produces a flux and this is the principle by which a simple AC generator operates. 
• In an AC generator electrical energy is generated from mechanical energy. It is made up of a coil fixed onto a rotor shaft. The direction of the magnetic field is kept perpendicular to the axis of rotation of the coil. Using external means, the coil is mechanically rotated in the uniform magnetic field. The magnetic flux through the coil changes due to the rotation of the coil and an EMF is induced in the coil. Thus, electrical energy is generated from mechanical energy.

Conclusion

• Faraday’s discoveries and induction laws have made a significant impact in our understanding of electromagnetic induction. He came up with 3 experiments to establish Faraday’s laws. 
• The first experiment shows that relative motion between a magnet and a coil generates an induced current which disappears when the relative motion stops.
• The second experiment shows that an induced current is generated when a coil connected to a battery with a stable magnetic field moves between another coil.
• The third displays that relative motion is not required for generation of induced current and that a change in magnetic flux is sufficient.

Finally, the working of AC generators based on Faraday’s law is explained.