Michael Faraday and Joseph Henry performed experiments independently and explained that the electric field produced (induced) from time varying magnetic field can produce electric current in closed coil. This phenomenon is called electromagnetic induction.

After the experiments of Henry various applications of electromagnetic induction are known. For example, the generators used at our work places to provide electric supply are based on electromagnetic induction. Electric guitars also work with the use of this phenomenon. This phenomenon is also used to melt metals fastly and safely. These days induction cookers are also popular and are replacing the traditional gas stoves. In this chapter, we will learn about the principles related to electromagnetic induction.

Faraday’s Laws of Electromagnetic Induction:

On the basis of Faraday’s experiments on electromagnetic induction, he gave two laws which are called Faraday’s laws electromagnetic induction.

First Law: Whenever the amount of magnetic flux linked with a closed circuit changes, an emf is induced in it which lasts only so long as the change in flux is taking place.
Lines of field increase - Inverse current
Lines of field decrease - Direct current

Second Law: According to this law, “the magnitude of induced emf is equal to the rate of change of magnetic flux.” If the induced emf is represented by ε, then mathematically,
ε = \(\frac{d \phi_{B}}{d t}\) …………… (1)
If N is the number of turns in coil and the turns in coil are nearby, then, the flux related to each turn uniformly changes. Thus, total induced emf,
ε = \(\frac{N d \phi_{B}}{d t}\) …………… (2)
Substituting ϕ_B = BA cos θ
The flux in a coil can be changed by :
(i) Changing the magnetic field B in coil,
(ii) Changing the total area of coil or that area of the coil which is in magnetic field.
For example, expanding or contracting the coil for pushing it in or drawing it out.
(iii) Changing the angle between the magnetic field B and the normal of the plane of coil (or in the plane of coil). For example, rotating the coil so that initially, B is normal to the surface and then, it is along the plane.