Faraday's Law

When we study the topic of electromagnetism, we come across one of the important laws called Faraday’s Law which basically describes the key points leading to the practical generation of electricity or electromagnetic induction.

The law was proposed in the year 1831 by an experimental physicist and chemist named Michael Faraday. So you can see where the name of the law comes from. That being said, the Faraday’s law or laws of electromagnetic induction are basically the results or the observations of the experiments that Faraday conducted. He performed three main experiments to discover the phenomenon of electromagnetic induction.

Faraday's Law

Faraday’s Experiment:

Relationship Between Induced EMF and Flux:

In the first experiment, he proved that when the strength of the magnetic field is varied then only the induced current is produced. An ammeter was connected to a loop of wire; the ammeter deflected when a magnet was moved towards the wire.

In the second experiment he proved that passing a current through an iron rod would make it electromagnetic. He observed that when there a relative motion exists between the magnet and the coil, an induced electromagnetic force is created. When the magnet was rotated about its axis, no electromotive force was observed but when the magnet was rotated about its own axis then the induced electromotive force was produced. Thus, there was no deflection in the ammeter when the magnet was held stationary.

While conducting the third experiment, he recorded that galvanometer did not show any deflection and no induced current was produced in the coil when the coil was moved in a stationary magnetic field. The ammeter deflected in the opposite direction when the magnet was moved away from the loop.

Faraday's Experiment

Position of Magnet Deflection in Galvanometer
Magnet at Rest No deflection in the galvanometer
Magnet moves towards the coil Deflection in the galvanometer in one direction
Magnet is held stationary at same position( near the coil) No deflection galvanometer
Magnet moves away from the coil Deflection in galvanometer but in opposite direction
Magnet held stationary at same position(away from the coil) No deflection in galvanometer

Conclusion:

After conducting all the experiments, Faraday finally concluded that if relative motion existed between a conductor and a magnetic field, the flux linkage with a coil changed and this change in flux produced voltage across a coil.

Faraday law basically states, “when the magnetic flux or the magnetic field changes with time, the electromotive force is produced”. Additionally, Michael Faraday also formulated two laws on the basis of above experiments.

Faraday’s First Law:

Faraday’s First Law of Electromagnetic Induction states that whenever a conductor is placed in varying magnetic field, electromagnetic fields are induced known as induced emf. If the conductor circuit is closed, a current is also induced which are called induced current.

Ways of changing magnetic field:

  • By rotating the coil relative to the magnet.
  • By moving the coil into or out of the magnetic field.
  • By changing the area of a coil placed in the magnetic field.
  • By moving a magnet towards or away from the coil.

Faraday’s Second Law:

Faraday’s Second Law of Electromagnetic Induction states that the induced emf in a coil is equal to the rate of change of flux linkage. Here the flux is nothing but the product of number of turns in the coil and flux connected with the coil.

Faraday’s law is represented as;

\(\varepsilon =-N\frac{\Delta \phi }{\Delta t}\)

In any case, Faraday’s law today finds its application in most of the electrical machines, industries and medical field etc.

Additionally, there is another key law known as Lenz’s law that describe electromagnetic induction as well.

Stay tuned with Byju’s to learn more about electromagnetic induction and much more.


Practise This Question

A square loop of side 4 cm is lying on a horizontal table. A uniform magnetic field of 0.5 T is directed downwards at an angle of 60o to the vertical as shown in Fig. 25.3. If the field increases from zero to its final value in 0.2 s, the emf induced in the loop will be