Science Class 12 - Electromagnetic Induction Notes

Electromagnetic Induction

Welcome to the chapter on Electromagnetic Induction for Class 12. In this chapter, you will learn about the phenomenon of electromagnetic induction, Faraday's laws, Lenz's law, and their applications in daily life and technology. By the end of this chapter, you will be able to explain how electric currents are produced by changing magnetic fields and solve related numerical problems.

Introduction

Electromagnetic induction is the process of generating an electric current by changing the magnetic field around a conductor. This principle is the foundation of many electrical devices such as generators and transformers.

Key Concepts

• Magnetic Flux (Φ): The total number of magnetic field lines passing through a given area.
• Induced EMF: The electromotive force generated in a conductor due to a changing magnetic field.
• Faraday's Laws: Laws that describe how an EMF is induced in a circuit.
• Lenz's Law: The direction of induced current opposes the change causing it.

Faraday's Laws of Electromagnetic Induction

• First Law: Whenever the magnetic flux linked with a circuit changes, an EMF is induced in the circuit.
• Second Law: The magnitude of the induced EMF is equal to the rate of change of magnetic flux through the circuit.
  Mathematically:
  EMF (ε) = -dΦ/dt

Lenz's Law

Lenz's law states that the direction of the induced current is such that it opposes the change in magnetic flux that produced it. This is why the negative sign appears in Faraday's law.

Factors Affecting Induced EMF

• Rate of change of magnetic flux
• Number of turns in the coil
• Area of the coil
• Strength of the magnetic field

Applications of Electromagnetic Induction

• Electric generators
• Transformers
• Induction cooktops
• Electric bells
• Credit card readers

Practice Questions

1. State Faraday's first and second laws of electromagnetic induction.
2. Explain Lenz's law with an example.
3. A coil of 100 turns is placed in a magnetic field. If the magnetic flux changes by 0.02 Wb in 0.1 s, calculate the induced EMF.
4. List two applications of electromagnetic induction in daily life.
5. Why is the negative sign used in Faraday's law?

Challenge Yourself

• Describe an experiment to demonstrate electromagnetic induction using a coil and a magnet.
• Derive the expression for the EMF induced in a rotating coil in a uniform magnetic field.

Did You Know?

• Michael Faraday discovered electromagnetic induction in 1831.
• All electricity generated in power plants is based on electromagnetic induction.

Glossary

• Electromagnetic Induction: The process of generating an EMF by changing the magnetic field around a conductor.
• Magnetic Flux: The measure of the magnetic field passing through a given area.
• EMF (Electromotive Force): The voltage generated by changing magnetic fields.
• Induced Current: The current produced due to induced EMF.

Answers to Practice Questions

1. First Law: An EMF is induced when the magnetic flux linked with a circuit changes.
   Second Law: The magnitude of the induced EMF is equal to the rate of change of magnetic flux through the circuit.
2. Lenz's law: If you move a magnet towards a coil, the induced current in the coil creates a magnetic field that opposes the motion of the magnet.
3. Induced EMF = (Number of turns × Change in flux) / Time = (100 × 0.02) / 0.1 = 20 V
4. Electric generators, transformers (any two).
5. The negative sign shows that the induced EMF opposes the change in magnetic flux (Lenz's law).

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Understanding electromagnetic induction helps you see how electricity is generated and used in the world around you!