Chapter 13: Sound

These NCERT Class 8 Science Chapter 13 notes explain the concept of sound in a clear and structured manner. The chapter focuses on how sound is produced by vibrations and how it travels through different media.

It discusses sound waves, parts of the human ear and how we hear sound. The chapter also explains audible range, infrasound, ultrasound and practical uses of ultrasound in medicine and industry.

Chapter 13 – Sound is important for understanding wave motion, hearing mechanism and noise pollution. It is highly relevant for school examinations and foundation level competitive preparation.

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1. Introduction: what is sound?

• Sound is a form of energy that produces the sensation of hearing.
• Sound is produced due to vibrations of objects.
• We hear sound through our ears.
• Sound helps in communication between living beings.
• When a school bell rings, its vibration produces sound.

2. How is sound produced?

• Sound is produced when an object vibrates.
• Vibration means to move back and forth rapidly.
• Vibrating strings of a guitar produce sound.
• The diaphragm of a drum vibrates to create sound.
• Vocal cords vibrate when we speak.

3. Sound needs a medium to travel

• Sound travels through a medium such as solids, liquids and gases.
• It cannot travel in a vacuum where there is no matter.
• Sound travels fastest in solids and slowest in gases.
• Air is the most common medium for sound on Earth.
• Astronauts cannot hear in space due to absence of medium.

4. Sound waves

• Sound travels in the form of sound waves.
• Sound waves are longitudinal waves.
• In longitudinal waves, particles vibrate in the direction of wave movement.
• Sound waves transfer energy but not matter.
• The speed of sound depends on the medium.

5. Human ear and its parts

• The human ear helps in hearing and balancing.
• The outer ear collects sound waves.
• The eardrum vibrates when sound waves strike it.
• The middle ear contains hammer, anvil and stirrup bones that amplify sound.
• The inner ear converts vibrations into signals sent to the brain through the auditory nerve.

6. Audible and inaudible sounds

• Audible sound is sound that humans can hear.
• The audible range for humans is from 20 Hz to 20,000 Hz.
• Infrasound has frequency less than 20 Hz.
• Ultrasound has frequency greater than 20,000 Hz.
• Humans cannot hear infrasound and ultrasound.

7. Uses of ultrasound

• Ultrasound is used in medical imaging or sonography.
• It helps in breaking kidney stones.
• It is used to detect cracks in metal blocks.
• It is used for cleaning delicate electronic parts.
• Doctors use ultrasound to observe a baby in the womb.

8. Noise and music

• Music is a pleasant sound with regular vibrations.
• Noise is an unpleasant sound with irregular vibrations.
• Music creates comfort and enjoyment.
• Noise can disturb mental peace.
• The difference lies in the pattern of vibrations.

9. Noise pollution and its effects

• Noise pollution is the presence of excessive or unwanted sound.
• Major sources include vehicles, factories and loudspeakers.
• Construction activities also produce noise pollution.
• It can cause headache, stress and hearing loss.
• Long exposure to noise affects health.

10. Measures to control noise pollution

• Avoid unnecessary honking on roads.
• Use silencers in vehicles to reduce noise.
• Restrict loudspeakers, especially near hospitals and schools.
• Plant trees to absorb sound.
• Use soundproof materials in buildings.

11. Key exam-oriented keywords explained

• Sound: Form of energy produced by vibrations.
• Vibration: Rapid back and forth movement of an object.
• Medium: Substance through which sound travels.
• Sound waves: Waves produced by vibrating objects to carry sound energy.
• Human ear: Organ that helps in hearing.
• Eardrum: Thin membrane that vibrates when sound waves strike it.
• Audible sound: Sound that humans can hear within 20 Hz to 20,000 Hz.
• Infrasound: Sound with frequency below 20 Hz.
• Ultrasound: Sound with frequency above 20,000 Hz.
• Noise: Unpleasant sound.
• Noise pollution: Excessive or unwanted sound harmful to health.

12. One-page summary for quick revision

• Sound is produced by vibrating objects.
• Sound needs a medium to travel and cannot move in vacuum.
• The human ear helps in hearing sound.
• Audible range is 20 Hz to 20,000 Hz.
• Noise pollution is harmful and must be controlled.

Understanding NCERT Class 8 Science Chapter 13 is essential to learn how sound is produced, transmitted and heard. The chapter clearly explains sound waves, human ear structure and noise pollution control.

The concepts help students understand real-life applications of sound and environmental concerns. It is highly useful for school exams and foundation competitive preparation.

Continue reading NCERT Class 8 Science Chapter 14 – Chemical Effects of Electric Current to understand electrolysis and electroplating.

FAQs

Q1. What is sound?
Sound is a form of energy produced by vibrating objects.

Q2. Can sound travel in vacuum?
No, sound cannot travel in vacuum because it needs a medium to travel.

Q3. What is the audible range for humans?
The audible range for humans is from 20 Hz to 20,000 Hz.

Q4. What is ultrasound?
Ultrasound is sound with frequency higher than 20,000 Hz and is used in medical imaging and industry.

Q5. Why is this chapter important for exams?
It explains sound production, wave motion and hearing mechanism, which are important for school exams and foundation preparation.

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