Question

The phenomenon of electromagnetic induction is:
A. The process of changing a body
B. The process of generating magnetic field due to current passing through a coil
C. Producing induced current in a coil due to relative motion between a magnet and the coil
D. The process of rotating a coil of an electric motor

Answer 1

Hint: First write down the definition of electromagnetic induction. We will check the mechanism and laws behind electromagnetic induction. Make a rough figure and write the related formula, i.e., $\epsilon =-{\displaystyle \frac{d\varphi }{dt}}$ and then conclude the answer.

Formula used: $\epsilon =-{\displaystyle \frac{d\varphi }{dt}}$

Complete step by step solution:
It was found experimentally by the scientists that when a coil conducts current it produces some magnetic fields as well. This was the magnetic effect of a conducting wire or coil. But could the reverse be true as well? If a wire or coil is placed in a magnetic field, will the coil start to conduct current automatically?
Well, Faraday found that when a coil is kept in a changing or varying magnetic field, it can conduct current. The wire actually generates some electromotive force within itself. This phenomenon was termed as electromagnetic induction.

If $\varphi$ be the magnetic flux linked with a coil, then its value will be different for different positions of its nearby magnet. So, if the magnet be moving, the flux changes, and the generated electromotive force is given by,
$\epsilon =-{\displaystyle \frac{d\varphi }{dt}}$
Sometimes, an ‘n’ is written on the right side of the equation to represent the number of turns on the coil.
 Hence, whenever there is a relative velocity between a coil and a magnet, an electromotive force is generated in the coil which generates current. This is called electromagnetic induction.
Hence, option C is the correct answer.

Additional information:
The principle of electromagnetic induction is used in Induction Oven, Electric Brakes, Dynamo etc. Lentz's law states that the electromotive force generated by a changing magnetic field tries to stop the cause of its own generation. This principle is widely used in circuit inductors and transformers.

Note: Remember the following things:
1. Never confuse electromagnetic induction with the magnetic effect of a conducting wire. They are two opposite events.
2. When the magnet and coil are kept close at a fixed distance, there will be no current. They must be in relative motion.
3. The faster one moves the magnet, more current is generated.