CBSE Class 8 Science Exemplar Chapter 13: Sound NCERT Solutions

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NCERT Solutions PDF Class 8 PDF

CBSE Class 8 Science Chapter 13, Sound, introduces students to the fascinating world of sound. This chapter explores how sound is generated through vibrations and why it needs a medium like air, water, or solids to travel. You'll learn about the characteristics of sound, including how factors like amplitude influence its loudness and how frequency relates to the time it takes for a sound wave to complete one cycle. The solutions also cover the speed at which sound travels through different materials and compare it with the much faster speed of light. Understanding these concepts is crucial for grasping wave phenomena and preparing for your science exams.

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Quick info

BoardCBSE
ClassClass 8
SubjectScience Exemplar
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 13

Chapter summary

Chapter 13 of the Class 8 Science Exemplar NCERT Solutions focuses on the topic of Sound. It covers essential concepts such as sound production through vibrations, the requirement of a medium for sound travel, and the distinction between sound and light propagation. The solutions also explain how the amplitude of a sound wave determines its loudness and how to calculate the time period from frequency. The exercises reinforce understanding of these principles, aiding students in grasping the physics of sound.

Learning outcomes

  • Understand that sound is produced by vibrations.
  • Identify the mediums through which sound can travel.
  • Explain that sound requires a medium for propagation.
  • Relate the loudness of sound to its amplitude.
  • Calculate the time period of an object based on its frequency.
  • Differentiate between the propagation of sound and light.

Topics covered

Paper topics

  • Sound Production
  • Vibrations
  • Medium for Sound Propagation
  • Vacuum
  • Loudness of Sound
  • Amplitude
  • Frequency
  • Time Period
  • Speed of Sound
  • Comparison of Sound and Light

Important topics

  • Sound Propagation
  • Amplitude and Loudness
  • Frequency and Time Period
  • Sound vs. Light

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Questions and Solutions

Multiple Choice Questions - 1

A list of mediums is given below:
  1. wood
  2. water
  3. air
  4. vacuum
In which of these mediums can sound travel?
  1. i & ii only
  2. i, ii & iii only
  3. iii & iv only
  4. ii, iii & iv only
Solution:

The correct option is (b) i, ii & iii only.

Sound waves are mechanical waves, meaning they require a medium to propagate from one point to another. They can travel through solids, liquids, and gases. In the given list, wood (solid), water (liquid), and air (gas) are all mediums through which sound can travel. Vacuum, however, is the absence of any medium, and therefore, sound cannot travel through it.

Multiple Choice Questions - 2

The loudness of sound depends on:
  1. its amplitude.
  2. its frequency.
  3. its time period.
  1. its speed.
Solution:

The correct option is (a) its amplitude.

The loudness of a sound is directly related to the amplitude of the sound wave. Amplitude is the maximum displacement or distance moved by a point on a vibrating body or wave measured from its equilibrium position. A sound wave with a larger amplitude carries more energy and is perceived as louder, while a sound wave with a smaller amplitude is perceived as softer or feeble.

Multiple Choice Questions - 3

Which of the following statements are correct?
  1. Sound is produced by vibrations.
  2. Sound requires a medium for propagation.
  3. Light and sound both require a medium for propagation.
  4. Sound travels slower than light.
  1. i & ii only
  2. i, ii & iii only
  3. ii, iii & iv only
  4. i, ii & iv only
Solution:

The correct option is (d) i, ii & iv only.

Let's analyze each statement:

  1. Sound is produced by vibrations: This statement is correct. Sound is generated when an object vibrates, creating disturbances in the surrounding medium.
  2. Sound requires a medium for propagation: This statement is correct. Sound waves are mechanical waves and need a medium (solid, liquid, or gas) to travel.
  3. Light and sound both require a medium for propagation: This statement is incorrect. While sound requires a medium, light waves are electromagnetic and can travel through a vacuum.
  4. Sound travels slower than light: This statement is correct. Light travels at an extremely high speed (approximately 3 x 108 m/s in a vacuum), whereas sound travels much slower, with its speed depending on the medium (e.g., about 343 m/s in air at room temperature).

Therefore, statements i, ii, and iv are correct.

Multiple Choice Questions - 4

An object is vibrating at 50 hertz. What is its time period?
  1. 0.02 s (b) 2 s
  2. 0.2 s
  3. 20.0 s
Solution:

The correct option is (a) 0.02 s.

The frequency of an object is the number of vibrations it completes in one second. The time period is the time taken to complete one vibration. The relationship between frequency (f) and time period (T) is given by:

T = \frac{1}{f}

Given that the frequency (f) is 50 hertz (Hz), we can calculate the time period (T) as follows:

T = \frac{1}{50 \text{ Hz}}

T = 0.02 \text{ s}

Therefore, the time period of the object is 0.02 seconds.

Common mistakes

  • Assuming sound can travel through a vacuum.
  • Confusing the relationship between amplitude and loudness.
  • Incorrectly applying the formula for time period.
  • Mistaking light and sound for having similar propagation requirements.

Revision tips

  • Review the definition of vibration and its role in sound production.
  • Memorize the mediums through which sound travels and those it cannot.
  • Understand the direct relationship between amplitude and loudness.
  • Practice calculating time period using the frequency formula.
  • Compare and contrast the properties of sound and light waves.

Practice MCQs

Q1. Which of the following mediums can support the travel of sound?

Q2. The loudness of a sound is primarily determined by:

Q3. Which of the following statements about sound and light is correct?

Q4. If an object vibrates at a frequency of 50 Hz, what is its time period?

Frequently asked questions

What is sound, and how is it produced?

Sound is a form of energy that travels as waves. It is produced when an object vibrates, causing the surrounding medium to vibrate as well.

Can sound travel through a vacuum?

No, sound cannot travel through a vacuum. It requires a medium such as a solid, liquid, or gas to propagate.

What is the relationship between loudness and amplitude?

The loudness of a sound is directly related to the amplitude of the sound wave. A larger amplitude means a louder sound, while a smaller amplitude means a softer sound.

How is the time period of a sound wave calculated?

The time period (T) is the time taken for one complete vibration. It is the reciprocal of the frequency (f), calculated as T = 1/f.

Does sound travel faster or slower than light?

Sound travels much slower than light. Light travels at an extremely high speed, while sound's speed depends on the medium it travels through.

What are the different mediums through which sound can travel?

Sound can travel through solids (like wood), liquids (like water), and gases (like air).

Important links

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