Electromagnetic Induction is one of the most important chapters of Class 12 Physics. It forms the foundation of many electrical devices such as generators, transformers, induction motors, and electric power systems. This chapter explains how electric current is produced by changing magnetic fields, which is a key concept in modern physics and engineering.
For CBSE board exams, JEE Main, JEE Advanced, and other competitive exams, questions from this chapter are frequently asked in the form of numericals, derivations, and conceptual MCQs.
In these Electromagnetic Induction Class 12 Notes PDF, every topic is explained clearly with definitions, formulas, explanations, and applications so that students can understand concepts easily and score high marks.
Electromagnetic Induction Class 12 Notes PDF | CBSE Physics
1. Magnetic Flux (Φ)
Definition
Magnetic flux is the measure of the number of magnetic field lines passing through a given surface.
Formula
\Phi = B A \cos \theta
Where:
- B = magnetic field strength
- A = area of the surface
- θ = angle between magnetic field and normal to the surface
SI Unit
Weber (Wb)
Important Points
- Flux is maximum when θ = 0°
- Flux is zero when θ = 90°
- Magnetic flux can be positive or negative depending on orientation
2. Electromagnetic Induction
Definition
Electromagnetic induction is the phenomenon in which an electromotive force (EMF) is induced in a conductor or circuit when the magnetic flux linked with it changes.
Methods to Change Magnetic Flux
- Changing magnetic field strength
- Changing area of the coil
- Rotating the coil
- Moving a magnet towards or away from the coil
3. Faraday’s Laws of Electromagnetic Induction
First Law
Whenever the magnetic flux linked with a circuit changes, an induced EMF is produced in the circuit.
Second Law
The magnitude of induced EMF is directly proportional to the rate of change of magnetic flux.
Mathematical Expression
e = -\frac{d\Phi}{dt}
The negative sign represents Lenz’s Law.
4. Lenz’s Law
Statement
The direction of induced current is such that it opposes the cause that produces it.
Importance
- Explains the direction of induced current
- Supports the law of conservation of energy
Example
When a magnet approaches a coil, the induced current produces a magnetic field that repels the magnet.
5. Fleming’s Right-Hand Rule
This rule helps to find the direction of induced current.
Procedure
Stretch:
- Thumb → direction of motion of conductor
- First finger → magnetic field direction
- Middle finger → induced current direction
6. Induced EMF
Definition
Induced EMF is the voltage produced due to a change in magnetic flux.
Types of Induced EMF
- Statically Induced EMF
- Dynamically Induced EMF
7. Motional EMF
When a conductor moves in a magnetic field, EMF is induced.
Formula
e = B l v
Where:
- l = length of conductor
- v = velocity of motion
8. Eddy Currents
Definition
Eddy currents are circulating currents induced in bulk conductors when magnetic flux changes.
Applications
- Electromagnetic braking
- Induction furnace
- Speedometers
Disadvantages
- Energy loss as heat
- Reduced efficiency
Reduction
- Laminated cores
- Slotted conductors
9. Self Induction
Definition
The phenomenon in which a changing current in a coil induces EMF in the same coil.
Self Inductance (L)
e = -L \frac{dI}{dt}
SI Unit
Henry (H)
10. Mutual Induction
Definition
When a changing current in one coil induces EMF in a nearby coil, it is called mutual induction.
Formula
e = -M \frac{dI}{dt}
Where M is mutual inductance.
11. Coefficient of Mutual Induction
Definition
Mutual inductance is defined as the induced EMF in one coil due to unit rate of change of current in another coil.
SI Unit
Henry (H)
12. Energy Stored in an Inductor
When current flows through an inductor, energy is stored in its magnetic field.
Formula
U = \frac{1}{2} L I^2
13. AC Generator (Alternator)
Principle
Based on Faraday’s law of electromagnetic induction.
Main Components
- Armature coil
- Field magnet
- Slip rings
- Brushes
Working
When the coil rotates in a magnetic field, alternating EMF is produced.
14. Important Derivations (Exam-Oriented)
- Expression for induced EMF
- Motional EMF derivation
- Energy stored in an inductor
- EMF of a rotating coil
15. Important Questions (Repeated in Exams)
- State Faraday’s laws of electromagnetic induction.
- Explain Lenz’s law with an example.
- What are eddy currents? Write two applications.
- Define self and mutual inductance.
- Derive expression for energy stored in an inductor.
- Explain the working of an AC generator.
Conclusion
Electromagnetic Induction is a conceptual yet scoring chapter if studied properly. Understanding magnetic flux, Faraday’s laws, Lenz’s law, and inductance makes it easier to solve numericals and derivations.
These Electromagnetic Induction Class 12 Notes PDF are designed to help students prepare efficiently for board exams and competitive exams.
Repeated & Important Questions – Electromagnetic Induction Class 12
Very Short Answer Questions (1 Mark)
- What is electromagnetic induction?
- Define magnetic flux and write its SI unit.
- What is the SI unit of induced EMF?
- State Lenz’s law.
- What is self inductance?
- Write the SI unit of mutual inductance.
- What happens to induced current when magnetic flux remains constant?
Short Answer Questions (2–3 Marks)
- State Faraday’s first and second laws of electromagnetic induction.
- Explain the significance of the negative sign in Faraday’s law.
- What is motional EMF? Write its formula.
- Define eddy currents. Write any two applications.
- Distinguish between self induction and mutual induction.
- Why laminated iron cores are used in transformers?
- What is Fleming’s right-hand rule? State its use.
Long Answer Questions (4–5 Marks)
- Explain Faraday’s laws of electromagnetic induction with suitable examples.
- State and explain Lenz’s law. How does it support the law of conservation of energy?
- Derive an expression for the induced EMF in a conductor moving in a magnetic field.
- Derive the expression for energy stored in an inductor.
- Explain the principle, construction, and working of an AC generator with a neat diagram.
- What are eddy currents? Explain their advantages and disadvantages.
Numerical Problems (Frequently Asked)
- A coil of area A is placed in a uniform magnetic field B. Calculate magnetic flux when the plane of the coil is perpendicular to the field.
- A conductor of length l moves with velocity v in a magnetic field B. Find the induced EMF.
- Calculate the energy stored in an inductor of inductance L carrying current I.
- Find the induced EMF when magnetic flux changes uniformly with time.
Assertion–Reason / Conceptual Questions
- Assertion: Induced current always opposes the cause producing it.
Reason: Lenz’s law is based on the conservation of energy. - Assertion: Eddy currents cause energy loss.
Reason: Eddy currents produce heat in conductors.
Diagram-Based Repeated Questions
- Draw a labelled diagram of an AC generator and explain its working.
- Draw a diagram showing induced current when a magnet is moved towards a coil.
Most Important Exam Tip 🔥
📌 Lenz’s Law, Faraday’s Laws, Eddy Currents, AC Generator aur Energy Stored in Inductor
👉 Ye topics almost har saal repeat hote hain – theory + numericals dono me.