Question

What are the methods of producing induced emf?

Answer 1

To produce a current in a coil, we need to create potential difference across the ends of the wire. A method to create potential difference is with the help of electromagnetic induction. This is done using Faraday’s law of electromagnetic induction.

Complete step by step solution:
Faraday’s law of electromagnetic induction is a basic law of electromagnetism predicting how a magnetic field will interact with an electric circuit to produce an electromotive force or say potential difference across the ends of a wire. This phenomenon is called electromagnetic induction.
Faraday (scientist) observed that if magnetic flux linked with a circuit changes with time an emf will be induced in the circuit. So, we first need to understand what magnetic flux is.
Magnetic flux: is the measure of number of lines passing through an area A. The expression for magnetic field is given by
\phi = \overrightarrow B .\overrightarrow A \\\ = BA\cos \theta \\\ \\\ \
Where $\theta$ is the angle between the magnetic field and direction perpendicular to the cross sectional area of the circuit.
The magnitude of emf induced in the circuit is equal to the rate of change of magnetic flux linking with the circuit.
$EMF = - \dfrac{{d\phi }}{{dt}} \\\ \\\$

Minus sign is used as direction of induced emf is opposite to the cause producing change in magnetic field as stated by Lenz’s law.
There are three ways in which we can change the magnetic flux linking with the coil:
1 . Changing the magnetic field(B).
2 . Changing the area of circuital loop(A)
3 . Changing the angle $\theta$.
Let us now discuss one by one all the methods to induce emf.
Method 1:
The magnetic field can be changed by changing the current flowing in the electromagnet which is producing the magnetic field.
Method 2:
The area of the circuit can be changed by moving a section of the circuit in a magnetic field.
Method 3:
Angles can be changed by changing the circuital loop in the magnetic field.

Note: Finally, we can conclude that emf can be induced by changing magnetic flux linking with the coil by any of three methods stated above. Some important applications of induced emf are in generators, galvanometers and transformers. More is the rate of change of magnetic flux, more is the magnitude of induced emf.