# Electromagnetic Induction

Article Topics

Electromagnetic induction: It is the phenomenon of generating an emf by changing the number of magnetic lines of force (i.e. magnetic flux) associated with the circuit. The emf so generated is known as induced emf. If the circuit is closed the current which flows in it due to induced emf is known as induced current.

### Faraday’s law of electromagnetic induction

First law: Whenever the amount of magnetic flux linked with a circuit changes, an emf is induced in the circuit. This induced emf persists as long as the change in magnetic flux continues.

Second law: The magnitude of the induced emf is equal to the time rate of change of magnetic flux. Mathematically, induced emf is given by e = − df / dt

Lenz’s law: This law gives us the direction of induced emf. According to this law, the direction of induced emf in a circuit is such that it opposes the change in magnetic flux responsible for its production. Lenz’s law is in accordance with the principle of conservation of energy.

Fleming’s right-hand rule: Fleming’s right-hand rule also gives us the direction of induced emf or current, in a conductor moving in a magnetic field. According to this rule, if we stretch the forefinger, central finger and thumb of our right hand in mutually perpendicular directions such that forefinger points along the direction of the field and thumb is along the direction of motion of the conductor, then the central finger would give us the direction of induced current or emf.

### Applications of Lenz’s law

– When a north pole of a bar magnet is moved towards a coil, the current induced in the coil will be in an anticlockwise direction as shown in the figure.

– When a north pole of a bar magnet is moved away from the coil, the current induced in the coil will be in a clockwise direction as shown in the figure.

– When a current-carrying coil is moved towards a stationary coil, the direction of the current induced in the stationary coil is as shown in the figure.

– When a current-carrying coil is moved away from a stationary coil, the direction of the current induced in the stationary coil is as shown in the figure.

– When two coils A and B are arranged as shown in the figure, then on pressing K, current in A increases in a clockwise direction. Therefore, the induced current in B will be in an anticlockwise direction.

– However, when key K is released, current in A decreases in a clockwise direction. Therefore, the induced current in B will be in a clockwise direction.

– When the current in a straight conductor AB is increased, induced current in the loop will be in a clockwise direction as shown in the figure.

If the current in AB is decreasing, the induced current in the loop will be in an anticlockwise direction.