Faraday's Law of Electromagnetic Induction

In 1831, Michael Faraday, an English physicist gave one of the most basic laws of electromagnetism called Faraday's law of electromagnetic induction. This law explains the working principle of most of the electrical motors, generators, electrical transformers and inductors. This law shows the relationship between electric circuit and magnetic field. Faraday performs an experiment with a magnet and a coil. During his experiment, he found how emf is induced in the coil when flux linked with it changes.

Michael Faraday

Faraday's Experiment

RELATIONSHIP BETWEEN INDUCED EMF AND FLUX Faraday's law In this experiment, Faraday takes a magnet and a coil and connects a galvanometer across the coil. At starting, the magnet is at rest, so there is no deflection in the galvanometer i.e needle of galvanometer is at the center or zero position. When the magnet is moved towards the coil, the needle of galvanometer deflects in one direction. When the magnet is held stationary at that position, the needle of galvanometer returns back to zero position. Now when the magnet is moved away from the coil, there is some deflection in the needle but in opposite direction and again when the magnet becomes stationary, at that point with respect to coil, the needle of the galvanometer returns back to the zero position. Similarly, if magnet is held stationary and the coil is moved away and towards the magnet, the galvanometer shows deflection in similar manner. It is also seen that, the faster the change in the magnetic field, the greater will be the induced emf or voltage in the coil.
Position of magnetDeflection in galvanometer
Magnet at restNo deflection in galvanometer
Magnet moves towards the coilDeflection in galvanometer in one direction
Magnet is held stationary at same position (near the coil)No deflection in galvanometer
Magnet moves away from the coilDeflection in galvanometer but in opposite direction
Magnet is held stationary at same position (away from the coil)No deflection in galvanometer
Conclusion: From this experiment, Faraday concluded that whenever there is relative motion between conductor and a magnetic field, the flux linkage with a coil changes and this change in flux induces a voltage across a coil.
Michael Faraday formulated two laws on the basis of above experiments. These laws are called Faraday's laws of electromagnetic induction.

Faraday's Laws

Faraday's First Law

Any change in the magnetic field of a coil of wire will cause an emf to be induced in the coil. This emf induced is called induced emf and if the conductor circuit is closed, the current will also circulate through the circuit and this current is called induced current.
Method to change magnetic field:
  1. By moving a magnet towards or away from the coil
  2. By moving the coil into or out of the magnetic field.
  3. By changing the area of a coil placed in the magnetic field
  4. By rotating the coil relative to the magnet.

Faraday's Second Law

It states that the magnitude of emf induced in the coil is equal to the rate of change of flux that linkages with the coil. The flux linkage of the coil is the product of number of turns in the coil and flux associated with the coil.

Faraday Law Formula

Faraday's law Consider, a magnet is approaching towards a coil. Here we consider two instants at time T1 and time T2. Flux linkage with the coil at time, Flux linkage with the coil at time, Change in flux linkage, Let this change in flux linkage be, So, the Change in flux linkage Now the rate of change of flux linkage Take derivative on right hand side we will get
The rate of change of flux linkage But according to Faraday's law of electromagnetic induction, the rate of change of flux linkage is equal to induced emf.  Considering Lenz's Law.  Where, flux Φ in Wb = B.A
B = magnetic field strength
A = area of the coil

Applications of Faraday's Law

Faraday law is one of the most basic and important laws of electromagnetism. This law finds its application in most of the electrical machines, industries and medical field etc.

Video Presentation of Faraday's Law

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