NCERT Class 11 Physics Physics Part-II: Chapter 7 — 1 INTRODUCTION
This chapter introduces the concept of waves in NCERT Class 11 Physics Part-II. It explains that waves are disturbances that propagate through a medium or vacuum, transporting energy and information without the bulk transfer of matter. The chapter distinguishes between mechanical waves, which require a medium (like sound waves or waves on a string), and electromagnetic waves, which can travel through vacuum (like light). It also briefly mentions matter waves. Examples like ripples in water, sound propagation, and disturbances in a spring system illustrate wave motion. The chapter emphasizes that waves are fundamental to communication and have been studied scientifically since the 17th century, with key contributions from scientists like Huygens.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 11 |
| Subject | Physics |
| Book | Physics Part-II |
| Chapter | Chapter 7 — 1 INTRODUCTION |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 6 minutes |
| Word count | 1063 |
Learning outcomes
- Define waves and understand their role in energy and information transfer.
- Distinguish between mechanical waves and electromagnetic waves.
- Recognize examples of wave phenomena in everyday life.
- Understand the basic concept of wave propagation through a medium.
- Appreciate the importance of waves in communication systems.
Vocabulary
| Word | Meaning |
|---|---|
| Disturbance | A departure from a state of rest or equilibrium. |
| Propagates | To spread or extend outwards. |
| Medium | A substance or environment through which a wave travels. |
| Mechanical waves | Waves that require a material medium for propagation. |
| Electromagnetic waves | Waves that can travel through vacuum, such as light and radio waves. |
| Vacuum | A space entirely devoid of matter. |
| Oscillations | Regular and repeated variations or movements. |
| Compression | A region where particles are pushed closer together, increasing density and pressure. |
| Rarefaction | A region where particles are spread farther apart, decreasing density and pressure. |
| Matter waves | Waves associated with subatomic particles like electrons and protons. |
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Practice questions
- What is the fundamental difference between a wave and the bulk movement of a medium? Answer: A wave is a disturbance that travels through a medium, transporting energy and information without the actual physical transfer of matter as a whole. The bulk movement of a medium implies the entire mass of the medium is displaced.
- Give an example of a mechanical wave and explain why it is classified as such. Answer: Sound waves are mechanical waves because they require a medium (like air, water, or solids) to travel. They involve the oscillation of particles within the medium.
- Can light waves travel through vacuum? What type of waves are they? Answer: Yes, light waves can travel through vacuum. They are electromagnetic waves.
- What is the speed of electromagnetic waves in vacuum? Answer: The speed of electromagnetic waves in vacuum is c = 299,792,458 m/s.
Practice MCQs
Q1. Which of the following is NOT a type of wave mentioned in the chapter?
Explanation: The chapter discusses mechanical waves, electromagnetic waves, and matter waves. Gravitational waves are not mentioned in this introductory section.
Q2. When a pebble is dropped in a pond, the ripples that spread outward are an example of:
Explanation: Water waves are mechanical waves because they require the medium of water to propagate.
Q3. Which type of wave can travel through vacuum?
Explanation: Electromagnetic waves, like light, do not require a medium and can travel through the vacuum of space.
Q4. The disturbance in a spring system, where one end is pulled and released, travels to the other end. This is an example of:
Explanation: The disturbance propagating along the connected springs is a mechanical wave, as it requires the medium (the springs) and involves oscillations of its parts.
Q5. What is the primary function of a wave?
Explanation: Waves are characterized by their ability to transport energy and patterns of disturbance (information) from one point to another.
Frequently asked questions
What is a wave?
A wave is a disturbance that travels through a medium or vacuum, transporting energy and information without the bulk transfer of matter.
What is the difference between mechanical waves and electromagnetic waves?
Mechanical waves require a material medium (like air or water) to propagate, while electromagnetic waves can travel through vacuum (like light).
Give an example of a mechanical wave.
Sound waves traveling through air, or waves on a stretched string, are examples of mechanical waves.
Give an example of an electromagnetic wave.
Light waves, radio waves, and X-rays are examples of electromagnetic waves.
Do waves involve the movement of matter?
Waves involve the oscillation of particles of the medium, but not the bulk transfer of matter itself over long distances.
What is the speed of light in vacuum?
The speed of light (an electromagnetic wave) in vacuum is approximately 299,792,458 meters per second.
What are matter waves?
Matter waves are associated with constituents of matter, such as electrons and protons, and are part of quantum mechanics.
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NCERT Class 11 Physics — Physics Part-II — Chapter 7 — 1 INTRODUCTION. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.