Question

The phenomenon of electromagnetic induction is:
A. The process of charging a sphere
B. The process of producing magnetic field in a coil
C. The process of producing induced current in a coil whenever there is a relative motion between the coil and the magnet
D. The process of producing cooling effect

Answer 1

Hint: The process of electromagnetic induction is governed by Faraday’s law of electromagnetic induction. Michael Faraday found out that when a coil is placed in a changing magnetic flux, an electromotive force is produced in the coil which can give rise to a current under suitable conditions.

Formula used:
The emf $E$ generated in a coil placed in a changing magnetic flux is given by
$E=-\dfrac{d{{\phi }_{B}}}{dt}$
where $\dfrac{d{{\phi }_{B}}}{dt}$ is the rate of change of magnetic flux $\left( {{\phi }_{B}} \right)$ with time $\left( t \right)$.
The negative sign signifies that the emf produces a current in a direction such that it opposes the changing magnetic flux.

Complete step by step answer:
Michael Faraday discovered the phenomenon of electromagnetic induction. His law states that an emf is produced in a conducting coil whenever it is placed in a changing magnetic flux. When a load is connected with the coil, a current flows in the coil due to the emf.
The mathematical expression of Faraday’s Law of electromagnetic induction is as follows.
The emf $E$ generated in a coil placed in a changing magnetic flux is given by
$E=-\dfrac{d{{\phi }_{B}}}{dt}$
where $\dfrac{d{{\phi }_{B}}}{dt}$ is the rate of change of magnetic flux $\left( {{\phi }_{B}} \right)$ with time $\left( t \right)$.
The negative sign signifies that the emf produces a current in a direction such that it opposes the changing magnetic flux.
A magnet produces its own magnetic field and hence magnetic flux. When a coil is brought near the magnet and a relative motion is generated between the two by either moving the magnet or the coil, then the amount of magnetic flux linking through the coil changes. This change in magnetic flux produces an emf and hence, subsequent electric current in the coil. Therefore, current is said to be electromagnetically induced in the coil.
Hence, the correct option is C) The process of producing induced current in a coil whenever there is a relative motion between the coil and the magnet.

Note: Students should remember that only relative motion causes a change in the magnetic flux linking through the coil. Thus, if the magnet and coil are just kept beside each other, there will be no current induced in the coil since there is no relative motion. This concept is often used as a trick option to tempt students to go down the wrong thinking path.
The negative sign in the mathematical expression of Faraday’s law of electromagnetic induction is very important. It signifies that the emf produced tends to oppose the change in flux, that is, the effect opposes the cause. This is a basic property of many natural phenomena where the effect of the phenomenon tries to oppose its cause. Another such example is that friction (effect) arises only when there is relative motion between two surfaces (cause) and friction tries to oppose the relative motion (effect opposes cause).