NCERT Class 12 Physics Physics Part-I: Chapter 8 — 1 INTRODUCTION
This chapter, Electromagnetic Waves, introduces the concept of electromagnetic waves, building upon previous knowledge of electric currents, magnetic fields, and changing magnetic fields. It highlights James Clerk Maxwell's crucial contribution: a time-varying electric field also generates a magnetic field. Maxwell's equations, which unify electricity, magnetism, and light, predicted the existence of these waves. The chapter discusses the need for displacement current to resolve inconsistencies in Ampere's circuital law, particularly when charging a capacitor. It also touches upon the experimental verification by Hertz and the technological applications leading to modern communication. The broad spectrum of electromagnetic waves, from gamma rays to radio waves, is also presented. This chapter is essential for understanding the fundamental nature of light and modern communication technologies within the CBSE Physics curriculum.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 12 |
| Subject | Physics |
| Book | Physics Part-I |
| Chapter | Chapter 8 — 1 INTRODUCTION |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 4 minutes |
| Word count | 702 |
Learning outcomes
- Understand the concept of displacement current and its necessity.
- Explain Maxwell's contribution to electromagnetism and his equations.
- Describe the nature and propagation of electromagnetic waves.
- Recognize the unification of light as an electromagnetic wave.
- Identify the broad spectrum of electromagnetic waves and their applications.
Vocabulary
| Word | Meaning |
|---|---|
| Electromagnetic waves | Coupled time-varying electric and magnetic fields that propagate in space. |
| Displacement current | A current suggested by Maxwell to account for a time-varying electric field generating a magnetic field. |
| Maxwell's equations | A set of equations unifying the laws of electricity and magnetism. |
| Capacitor | A device that stores electrical energy in an electric field. |
| Ampere's circuital law | A law relating the magnetic field around a closed circuit to the electric current flowing through it. |
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Practice questions
- Who is credited with formulating Maxwell's equations? Answer: James Clerk Maxwell.
- What did Maxwell propose in addition to electric current that generates a magnetic field? Answer: A time-varying electric field also generates a magnetic field.
- What is the approximate speed of electromagnetic waves in vacuum? Answer: Approximately 3 × 10^8 m/s, the speed of light.
- What technological revolution did the understanding of electromagnetic waves lead to? Answer: The revolution in communication.
Practice MCQs
Q1. Who experimentally demonstrated the existence of electromagnetic waves?
Explanation: Heinrich Hertz experimentally demonstrated the existence of electromagnetic waves in 1885, confirming Maxwell's predictions.
Q2. Maxwell's equations unify which fundamental domains of physics?
Explanation: Maxwell's equations successfully unified the laws of electricity and magnetism, and led to the conclusion that light is an electromagnetic wave.
Q3. What term did Maxwell introduce to resolve an inconsistency in Ampere's circuital law?
Explanation: Maxwell introduced the concept of displacement current to make Ampere's circuital law consistent, especially in situations involving changing electric fields like in a charging capacitor.
Q4. The speed of electromagnetic waves in vacuum is approximately:
Explanation: Maxwell's equations predicted the speed of electromagnetic waves to be approximately 3 × 10^8 m/s, which is the speed of light.
Q5. Which of the following is NOT a form of electromagnetic wave according to the chapter's description of the spectrum?
Explanation: Sound waves are mechanical waves and require a medium to propagate, unlike electromagnetic waves such as gamma rays, radio waves, and visible light.
Frequently asked questions
What is the main idea introduced in Chapter 8 of NCERT Physics Part-I?
Chapter 8 introduces the concept of Electromagnetic Waves, building upon previous concepts of electricity and magnetism, and highlighting Maxwell's prediction of these waves.
What is displacement current?
Displacement current is a term introduced by Maxwell to describe the magnetic field generated by a time-varying electric field, which is crucial for the existence of electromagnetic waves.
What are Maxwell's equations?
Maxwell's equations are a set of fundamental equations that unify the laws of electricity and magnetism and predict the existence of electromagnetic waves.
What is the significance of Maxwell's work regarding light?
Maxwell's work led to the conclusion that light itself is an electromagnetic wave, unifying the fields of optics, electricity, and magnetism.
Who experimentally confirmed the existence of electromagnetic waves?
Heinrich Hertz experimentally demonstrated the existence of electromagnetic waves in 1885.
What is the range of the electromagnetic spectrum mentioned in the chapter?
The chapter mentions the spectrum stretching from gamma rays (wavelength ~10^-12 m) to long radio waves (wavelength ~10^6 m).
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NCERT Class 12 Physics — Physics Part-I — Chapter 8 — 1 INTRODUCTION. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.