Electromagnetic Induction

Notes

1.1 Electromagnetic Induction

Electromagnetic induction is the phenomenon of production of an emf in a conductor or coil when the magnetic flux linked with it changes.

If the circuit is closed, the induced emf produces an induced current.

Key idea

Change in magnetic flux→Induced emf

​

This phenomenon was experimentally established by Michael Faraday and independently studied by Joseph Henry.

1.2 Faraday and Henry Experiments

Experiment 1: Magnet and Coil

Consider a coil connected to a galvanometer.

N S

[ MAGNET ] → ((((((((

COIL

|

Galvanometer

Observations

Case 1: Magnet moves towards the coil

→ Galvanometer shows deflection.

Case 2: Magnet is stationary

→ No deflection.

Case 3: Magnet moves away from coil

→ Galvanometer deflects in the opposite direction.

Case 4: Magnet moves faster

→ Greater deflection.

Conclusion

An emf is induced whenever the magnetic flux linked with the coil changes.

1.3 Magnetic Flux

Magnetic flux represents the amount of magnetic field passing through a surface.

It is represented by:

Φ

B

​

For a uniform magnetic field:

Φ

B

​

=

B

⋅

A

​

Therefore:

Φ

B

​

=BAcosθ

​

where:

B = magnetic field

A = area

θ = angle between magnetic field and area vector.

SI Unit

weber (Wb)

​

Also:

1Wb=1Tm

2

​

1.4 Maximum and Minimum Magnetic Flux

From:

Φ

B

​

=BAcosθ

Maximum Flux

When:

θ=0

∘

then:

Φ

max

​

=BA

​

Zero Flux

When:

θ=90

∘

then:

Φ

B

​

=0

​

Important Exam Point

The angle θ is between magnetic field

B

and the area vector, not the plane of the coil.

1.5 Faraday's Laws of Electromagnetic Induction

First Law

Whenever the magnetic flux linked with a circuit changes, an emf is induced in the circuit.

If the circuit is closed, an induced current flows.

Second Law

The magnitude of induced emf is equal to the rate of change of magnetic flux.

∣ε∣=

​

dt

dΦ

B

…