CBSE Class 11 Physics Exemplar Chapter 14: Waves NCERT Solutions

Reviewed by NCERT Help Editorial Team · Updated on 29 Jul 2026

NCERT Solutions PDF Class 11 PDF

CBSE Class 11 Physics Exemplar, Chapter 14, introduces the fascinating world of Waves. This section offers comprehensive NCERT Solutions that break down key concepts. We explore the characteristics of water waves, how sound waves behave when they move from one medium to another, and what influences the speed of sound in air, such as temperature, humidity, and pressure. The solutions also clarify the fundamental quantities that are transferred when a wave travels. Furthermore, we examine the specific conditions necessary for mechanical transverse and longitudinal waves to propagate through various media. These detailed explanations are crafted to demystify complex wave phenomena, providing students with a solid understanding essential for their academic success and exam readiness.

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Quick info

Board	CBSE
Class	Class 11
Subject	Physics Exemplar
Session	2026
Language	English
Type	NCERT Solutions
Chapter	Chapter 14

Chapter summary

This chapter's NCERT Solutions for Class 11 Physics Exemplar (Chapter 14: Waves) offers explanations for multiple-choice questions. It covers the dual nature of water waves, how wavelength changes with speed in different media for sound waves, the influence of humidity and temperature on sound speed in air, and the energy transfer in longitudinal waves. It also clarifies the conditions for transverse and longitudinal wave propagation in various states of matter.

Learning outcomes

Understand the nature of water waves as both longitudinal and transverse.
Analyze how the wavelength of sound waves changes when they move to a medium with different speed.
Explain the factors affecting the speed of sound in air, including temperature and humidity.
Identify the quantity transmitted during the propagation of longitudinal waves.
Differentiate the conditions for the propagation of transverse and longitudinal waves in different media.

Topics covered

Paper topics

Nature of Water Waves
Longitudinal Waves
Transverse Waves
Sound Wave Propagation
Wavelength and Speed Relationship
Factors Affecting Speed of Sound (Temperature, Humidity)
Energy Transmission in Waves
Conditions for Wave Propagation

Important topics

Wave types (longitudinal vs. transverse)
Speed of sound in air (temperature and humidity effects)
Wavelength changes in different media
Energy transfer in wave motion
Conditions for transverse wave propagation

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Questions and Solutions

Question 1

Water waves produced by a motorboat sailing in water are:

(a) neither longitudinal nor transverse

(b) both longitudinal and transverse

(d) only transverse

Solution: Water waves generated by a motorboat exhibit characteristics of both longitudinal and transverse waves. This is because the motion of water particles involves both displacement parallel to the direction of wave propagation (longitudinal) and displacement perpendicular to it (transverse). Therefore, the correct option is (b).

Question 2

Sound waves of wavelength $\lambda$ travelling in a medium with a speed of v m/s enter into another medium where its speed is 2v m/s. What is the wavelength of sound waves in the second medium?

(a) $\lambda$

(b) $\frac{\lambda}{\lambda}$

(d) $4\lambda$

Solution: The frequency of a wave remains constant when it passes from one medium to another. Let the frequency of the sound wave in the first medium be

f

and in the second medium be

f'

. Since frequency is constant,

f = f'

. We know the relationship between speed (

v

), frequency (

f

), and wavelength (

\lambda

) is

v = f\lambda

. In the first medium:

v = f\lambda

. In the second medium:

2v = f\lambda'

, where

\lambda'

is the wavelength in the second medium. Since

f

is the same in both mediums, we can write

f = \frac{v}{\lambda}

and

f = \frac{2v}{\lambda'}

. Equating the frequencies:

\frac{v}{\lambda} = \frac{2v}{\lambda'}

. Solving for

\lambda'

\lambda' = \frac{2v}{v} \lambda = 2\lambda

. Thus, the wavelength of the sound waves in the second medium is

2\lambda

. The correct option is (c).

Question 3

The speed of sound wave in air is:

(a) independent of temperature

(b) increases with pressure

(d) decreases with increase in humidity

Solution: The speed of sound in air is given by the formula

v = \sqrt{\frac{\gamma p}{\rho}}

, where

\gamma

is the adiabatic index,

p

is the pressure, and

\rho

is the density of air. While pressure and density are related, for an ideal gas at constant temperature, increasing pressure increases density proportionally, so speed is largely independent of pressure changes alone. However, humidity significantly affects the density of air. Moist air is less dense than dry air at the same temperature and pressure because the molar mass of water vapor (18 g/mol) is less than that of dry air (average ~29 g/mol). Since the speed of sound is inversely proportional to the square root of density (

v \propto \frac{1}{\sqrt{\rho}}

), a decrease in density due to increased humidity leads to an increase in the speed of sound. Temperature also affects the speed, with speed increasing as temperature increases (

v \propto \sqrt{T}

). Therefore, the speed of sound increases with an increase in humidity. The correct option is (c).

Question 4

A change in the temperature of the medium changes which property of sound waves?

(a) frequency of sound waves

(b) amplitude of sound waves

(d) loudness of sound waves

Solution: The speed of sound in a medium is dependent on its temperature. Specifically, the speed of sound in air is approximately proportional to the square root of the absolute temperature (

v \propto \sqrt{T}

). When the temperature of the medium changes, the speed of the sound wave changes. The relationship between speed (

v

), frequency (

f

), and wavelength (

\lambda

) is given by

v = f\lambda

. The frequency of a sound wave is determined by the source and does not change with the medium. Therefore, if the speed (

v

) changes due to a temperature variation, and the frequency (

f

) remains constant, the wavelength (

\lambda

) must change proportionally (

\lambda \propto v

). Loudness is related to amplitude, which is not directly determined by temperature change. Thus, a change in temperature primarily affects the wavelength of the sound waves. The correct option is (c).

Question 5

With the propagation of longitudinal waves through a medium, the quantity that is transmitted is:

(a) matter

(b) energy

(d) energy, matter and momentum

Solution: When longitudinal waves propagate through a medium, they transfer energy from one point to another. This energy transfer occurs through compressions and rarefactions in the medium. However, the particles of the medium themselves oscillate about their mean positions and are not transported along with the wave. Therefore, matter (mass) is not transmitted. Momentum is also not transmitted in a net sense over time, as particles oscillate back and forth. The primary quantity transmitted is energy. The correct option is (b).

Question 6

Which of the following statements are true for wave motion?

(a) Mechanical transverse waves can propagate through all mediums.

(b) Longitudinal waves can propagate through solids only.

(d) Longitudinal waves can propagate through vacuum.

Solution: Let's analyze each statement: (a) Mechanical transverse waves require a medium that can sustain shearing stress. Fluids (liquids and gases) do not have a definite shape and yield to shearing stress, so transverse waves cannot propagate through them. Thus, this statement is false. (b) Longitudinal waves involve compressions and rarefactions and can propagate through solids, liquids, and gases because all these states of matter can be compressed and expanded. Thus, this statement is false. (c) Mechanical transverse waves involve oscillations perpendicular to the direction of wave propagation, which requires the medium to have a shear modulus (ability to resist deformation of shape). Solids possess this property, allowing transverse waves to propagate. Fluids do not. Therefore, mechanical transverse waves can propagate through solids (and strings, which behave like solids in this context) but not fluids. This statement is true. (d) Longitudinal waves require a medium for propagation as they involve the oscillation of particles. Vacuum is devoid of matter, so waves cannot propagate through it. Thus, this statement is false. The correct statement is (c).

Common mistakes

Confusing the conditions for transverse wave propagation in solids and fluids.
Incorrectly assuming frequency changes when a wave enters a new medium.
Misunderstanding the relationship between sound speed, temperature, and humidity.

Revision tips

Focus on the conditions under which transverse and longitudinal waves can propagate.
Review the formulas relating wave speed, frequency, and wavelength, especially when changing mediums.
Understand the physical reasons behind how temperature and humidity affect sound speed in air.
Pay attention to the distinction between energy transfer and matter transfer in wave motion.

Practice MCQs

Q1. Water waves generated by a motorboat sailing in water exhibit which of the following characteristics?

Q2. A sound wave with wavelength $ $\lambda$ $ travels in a medium at a speed of $v$ m/s. When it enters a second medium where its speed is $2v$ m/s, what is the new wavelength?

Q3. Which of the following statements accurately describes the speed of sound waves in air?

Q4. When the temperature of the medium changes, which property of sound waves is most directly affected?

Q5. What is primarily transmitted through a medium during the propagation of longitudinal waves?

Q6. Mechanical transverse waves can propagate through which type of medium?

Frequently asked questions

What types of waves are water waves produced by a motorboat?

Water waves produced by a motorboat are both longitudinal and transverse. The particles of water exhibit both up-and-down (transverse) and back-and-forth (longitudinal) motions.

How does the wavelength of a sound wave change when it moves to a medium where the speed is doubled?

When a sound wave moves to a medium where its speed is doubled, and assuming the frequency remains constant, the wavelength also doubles. This is because wavelength is directly proportional to speed when frequency is constant ($\lambda \propto v$).

Does the speed of sound in air change with humidity?

Yes, the speed of sound in air increases with an increase in humidity. This is because moist air is less dense than dry air, and sound travels faster in less dense mediums.

What is the primary quantity transmitted by longitudinal waves?

The primary quantity transmitted by longitudinal waves is energy. The particles of the medium oscillate around their equilibrium positions but are not transported over long distances.

Can transverse waves travel through liquids?

No, mechanical transverse waves cannot propagate through fluids (liquids and gases). This is because fluids do not have a definite shape and cannot sustain the shearing stress required for transverse wave motion.

How does temperature affect the speed of sound in air?

The speed of sound in air increases with temperature. The speed is approximately proportional to the square root of the absolute temperature ($v \propto \sqrt{T}$).

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