Physics Electromagnetic Induction Notes Class 12 PDF

Electromagnetic Induction sounds way more complicated than it actually is. At first, it feels like, Why are magnets suddenly making electricity? But once the basic idea clicks, this chapter becomes surprisingly smooth.

This chapter from Physics Syllabus Class 12 revolves around one simple thing: if a magnetic field changes, electricity is produced. That’s literally the backbone of generators, transformers, and how electricity reaches our homes. So yeah, this isn’t just exam stuff - it’s real-life physics.

Class 12 Physics Electromagnetic Induction Notes

These Electromagnetic Induction Class 12 notes are made keeping exam pressure in mind. No heavy language, no textbook-style paragraphs. Just clean explanations, clear formulas, and examples that actually make sense.

Faraday’s laws, Lenz’s law, induced EMF, coils, generators - everything is explained the way you’d want it the night before an exam. Read once, Learn properly, revise fast.

What is Electromagnetic Induction?

Electromagnetic induction is just a name for something pretty simple - making electricity using a changing magnetic field. Whenever a magnetic field around a wire changes (like when you move a magnet near it or move the wire itself), an electric voltage gets produced in that wire. And if the circuit is closed, current starts flowing.

The key thing to remember is this: no change in magnetic field = no electricity.

Only when the magnetic flux changes, induction happens.

This idea was discovered by Michael Faraday in 1831, and honestly, this one concept explains how generators, transformers, charging systems, and power stations work today.

Faraday’s Laws of Electromagnetic Induction

Electromagnetic induction is all about how moving magnets or changing magnetic fields create electricity. Faraday’s Laws explain the rules behind this. Think of it like a recipe for electricity: change the magnetic field, and you get a current. 

1. Faraday’s First Law – The Basic Idea

In simple words: Whenever the magnetic field around a conductor changes, an EMF (electricity) is produced in the conductor.

Key points:

• If the magnetic field doesn’t change, no electricity is produced.
• Only changing magnetic fields create current.

Example you can imagine:

• Take a coil of wire and a bar magnet.
• Push the magnet into the coil → galvanometer needle moves.
• Pull the magnet out of the coil → needle moves in the opposite direction.
• Keep the magnet still inside → needle doesn’t move.

Why? Because only movement changes the magnetic field through the coil.

2. Faraday’s Second Law – How Much EMF

In simple words: The stronger the change in the magnetic field, the stronger the induced EMF.

Formula in text form: EMF = negative of (change in magnetic flux ÷ time)

Or, written clearly: EMF = - (ΔΦ / Δt)

Where:

• Φ = magnetic flux (how many magnetic field lines pass through the coil)
• ΔΦ / Δt = rate at which the flux changes
• Negative sign (-) = shows the direction of the induced current (this is Lenz’s Law)

Visual example:

• Push a magnet slowly through a coil → small current
• Push it fast → bigger current
• Pull it out quickly → current flows in opposite direction

Change the magnetic field → current is produced, Faster the change → bigger current

Lenz’s Law

Lenz’s Law tells us the direction of the induced current or EMF. Basically, whenever a magnetic field through a circuit changes, the induced current will always try to oppose that change. 

You can think of it like nature saying, Hey, I don’t like sudden changes! - kind of like how inertia resists motion. This is why there’s a negative sign in Faraday’s law - it shows this opposition.

Important Points to Remember:

• Induced EMF always opposes the change in magnetic flux.
• A negative sign in Faraday’s law represents this opposition.
• Helps conserve energy in electromagnetic systems.

Examples:

1. Pushing a magnet into a coil → induced current produces a magnetic field that pushes the magnet back.

2. Pulling a magnet out of a coil → induced current produces a magnetic field that pulls the magnet back in.

Ways to Change Magnetic Flux

Magnetic flux through a surface depends on the strength of the magnetic field, the area of the surface, and the angle between them. To induce an EMF or current, you need to change the flux, and there are a few simple ways to do this.

How Flux Can Change?

There are certain conditions based on which flux can change.

1. Change in Magnetic Field (B):

• Increasing or decreasing the magnetic field strength changes the flux.
• Example: Using a stronger or weaker magnet.

2. Change in Area (A):

• Changing the size or shape of the coil through which the field passes affects flux.
• Example: Stretching or compressing a coil.

3. Change in Orientation (θ):

• Rotating the coil relative to the magnetic field changes the angle, affecting the flux.
• Example: Turning the coil so it’s more or less aligned with the field.

4. Relative Motion Between Magnet and Coil:

• Moving the magnet toward or away from the coil changes how many field lines pass through, altering flux.
• Example: Sliding a bar magnet in and out of a coil.

Motion of Conductor in a Uniform Magnetic Field

When a conductor (like a wire) moves perpendicular to a magnetic field, the charges inside it experience a force. This force pushes the charges and creates an induced EMF. 

This phenomenon is called motional EMF. It’s the basic idea behind how generators produce electricity when coils rotate in a magnetic field.

Key Points and Formula:

Formula: e = B × l × v

• B → Magnetic field strength
• l → Length of the conductor inside the field
• v → Velocity of the conductor

Direction of Induced Current: Determined using Fleming’s Right-Hand Rule (Thumb → Motion, First finger → Field, Second finger → Current).

Practical Idea: Faster movement or a stronger magnetic field → more EMF is generated. This is exactly how generators and dynamos produce electricity.

Fleming’s Right-Hand Rule

When a conductor moves through a magnetic field, an electric current is generated. To figure out the direction of this induced current, we use Fleming’s Right-Hand Rule. Think of it as a simple hand trick that tells you which way the charges will flow.

Here’s how it works:

1. Thumb points in the direction of the conductor’s motion.

2. First finger points along the magnetic field (from North to South).

3. The second finger shows the direction of the induced current in the conductor.

A simple way to remember it is the mnemonic “M-F-C”, which stands for Motion-Field-Current. Make sure you always use your right hand, and remember, this rule is specifically for generators or situations involving motional EMF.

Eddy Currents

When a solid conductor is exposed to a changing magnetic flux, it doesn’t just let the current flow in one path like a normal wire. Instead, tiny circular currents are formed inside the conductor. These swirling currents are called eddy currents. They naturally appear whenever magnetic fields change through a solid material.

Effects of Eddy Currents

• They generate heat, which is energy lost from the system.
• They are used in induction furnaces to heat metals efficiently.
• They appear in speedometers to help measure speed.
• They provide damping in devices like balances and galvanometers, helping stabilize movements.

How to Reduce Eddy Currents?

To minimize energy loss, engineers use laminated iron sheets instead of solid ones. Thin sheets break up the loops, which weakens the eddy currents and reduces heating.

Self-Induction

Self-induction happens when the current in a coil changes. As the current changes, the magnetic field around the coil changes, and this changing field induces an EMF in the same coil that opposes the change in current. It’s like the coil is resisting sudden changes in current - nature doesn’t like abrupt changes!

Formula: EMF (e) = - L × (di/dt)

• L is the self-inductance of the coil (measured in Henry, H).
• The negative sign indicates that the induced EMF opposes the change in current.

For a solenoid, self-inductance can be calculated as: L = μ₀ × (N² × A) / l, where:

• μ₀ = permeability of free space
• N = number of turns
• A = cross-sectional area
• l = length of the solenoid

Self-induction is important in circuits with rapidly changing currents, like switching circuits or AC circuits with coils, because it can oppose sudden surges and protect devices.

Mutual Induction

Mutual induction occurs when two coils are placed close to each other. If the current in the first coil changes, it produces a changing magnetic field that passes through the second coil and induces an EMF in the second coil.

Formula: e₂ = - M × (di₁/dt)

M = mutual inductance between the coils.

Mutual inductance depends on:

• Number of turns in each coil
• Area of the coils
• Distance between the coils
• Magnetic coupling between the coils

Applications include transformers, induction coils, and AC power systems, where we need to transfer energy without direct electrical connection.

AC Generator (Dynamo)

An AC generator converts mechanical energy into electrical energy using electromagnetic induction.

• Principle: Rotating a coil in a magnetic field changes the magnetic flux through the coil, which induces an EMF.
• Parts: Coil, magnet, slip rings, brushes
• EMF generated: e = e₀ × sin(ωt)
• If the coil rotates with angular velocity ω:
  
  • Magnetic flux, Φ = B × A × cos(ωt)
  • Induced EMF, e = - dΦ/dt = B × A × ω × sin(ωt)

AC generators are used in power plants to supply electricity to homes and industries.

Transformer

A transformer is a device that works on the principle of mutual induction. It is used to increase or decrease AC voltage without changing its frequency.

• Working: Alternating current in the primary coil produces a changing magnetic flux, which induces EMF in the secondary coil.
• Transformer equation: Vp / Vs = Np / Ns = Is / Ip
• Vp, Vs = primary & secondary voltage
• Np, Ns = number of turns in primary & secondary coil
• Ip, Is = primary & secondary current

Types of transformers:

• Step-up → increases voltage
• Step-down → decreases voltage
• Energy losses in transformers: Eddy currents, hysteresis, copper loss, leakage flux
• How to minimize losses: Use laminated iron cores, soft iron, and thicker copper wires
• Applications: Power transmission, household transformers, voltage regulation in electronics

FAQs

Q1. What is electromagnetic induction?

Ans. Electromagnetic induction is the phenomenon in which an electric current is induced in a conductor when the magnetic flux linked with it changes.

Q2. What is magnetic flux?

Ans Magnetic flux is the measure of the total magnetic field passing through a given area. It depends on the magnetic field strength, area and the angle between them.

Q3. State Faraday’s laws of electromagnetic induction.

Ans. Faraday’s laws state that an EMF is induced whenever magnetic flux changes and the magnitude of induced EMF is proportional to the rate of change of magnetic flux.

Q4. What does Lenz’s law state?

Ans. Lenz’s law states that the direction of induced current is such that it opposes the change in magnetic flux that produces it.

Q5. Why is electromagnetic induction important?

Ans. It is the basic principle behind generators, transformers, induction cooktops and many electrical devices used in daily life.