Class 9 Science Sound Waves: Characteristics and Applications Solutions | New NCERT Answers

Sound is an essential part of our daily lives. From listening to music and communicating with others to hearing warning alarms, sound plays a crucial role in human life. Sound is produced by vibrations and travels through a medium in the form of waves.

The chapter "Sound Waves: Characteristics and Applications" in the New NCERT Class 9 Science textbook introduces students to the nature of sound, its properties, characteristics, and practical applications. Understanding sound waves helps students build a strong foundation for advanced Physics concepts.

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This article provides complete Class 9 Science Sound Waves: Characteristics and Applications Solutions, important questions, MCQs, and detailed explanations for exam preparation.

What is Sound?

Sound is a form of energy produced by vibrating objects.

Examples:

• Ringing bell

• Guitar strings

• Human vocal cords

• Drum membrane

When an object vibrates, it creates disturbances in the surrounding medium, producing sound waves.

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How is Sound Produced?

Sound is produced due to vibrations.

Examples:

• A plucked guitar string vibrates and produces sound.

• A struck tuning fork vibrates and creates sound waves.

• Human vocal cords vibrate while speaking.

Without vibration, sound cannot be produced.

Sound as a Wave

Sound travels through a medium as a longitudinal wave.

In longitudinal waves, particles of the medium vibrate parallel to the direction of wave propagation.

Sound cannot travel through a vacuum because there are no particles to transfer vibrations.

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Medium of Sound

Sound requires a material medium to travel.

Types of Medium

• Solids

• Liquids

• Gases

Sound travels fastest in solids and slowest in gases.

Example

• Railway tracks carry sound faster than air.

• Whales communicate through sound in water.

Characteristics of Sound Waves

The main characteristics of sound waves are:

1. Amplitude

Amplitude is the maximum displacement of particles from their mean position.

Higher amplitude means louder sound.

Example

• Loudspeaker at high volume has greater amplitude.

• Whispering has lower amplitude.

2. Frequency

Frequency is the number of vibrations produced in one second.

The SI unit of frequency is Hertz (Hz).

Formula

Frequency is represented as:

f = Number of vibrations per second

Example

• Human hearing range: 20 Hz to 20,000 Hz

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3. Time Period

Time period is the time taken to complete one vibration.

Formula:

T = 1/f

Where:

• T = Time Period

• f = Frequency

4. Wavelength

Wavelength is the distance between two consecutive compressions or rarefactions.

It is represented by λ (lambda).

The SI unit is meter (m).

5. Speed of Sound

The speed of sound depends on the medium.

Formula:

Speed = Frequency × Wavelength

Factors Affecting Speed

• Nature of medium

• Temperature

• Density

Loudness and Pitch

Loudness

Loudness depends upon amplitude.

Greater amplitude = Greater loudness

Examples:

• Loudspeaker

• Drum beats

Pitch

Pitch depends upon frequency.

Higher frequency = Higher pitch

Examples:

• Female voice generally has higher pitch than male voice.

• Mosquito sound has higher pitch.

Reflection of Sound

Reflection occurs when sound waves strike a surface and bounce back.

Examples:

• Echo

• Sound reflection in auditoriums

Echo

An echo is the repetition of sound caused by reflection.

Conditions for hearing an echo:

• Reflecting surface should be far enough.

• Time gap should be at least 0.1 second.

Examples:

• Mountains

• Large empty halls

Applications of Reflection of Sound

1. Megaphones

Used to direct sound in one direction.

2. Stethoscope

Doctors use it to hear internal body sounds.

3. Sound Boards

Used in auditoriums to improve sound quality.

4. Hearing Aids

Help people with hearing difficulties.

Ultrasonic Sound

Sounds having frequencies above 20,000 Hz are called ultrasonic sounds.

Humans cannot hear ultrasonic waves.

Applications

• Medical imaging

• SONAR

• Detecting cracks in metals

• Cleaning delicate instruments

SONAR (Sound Navigation and Ranging)

SONAR uses ultrasonic waves to detect underwater objects.

Uses

• Measuring ocean depth

• Locating submarines

• Detecting underwater obstacles

Important NCERT Questions and Answers

Q1. What is sound?

Answer: Sound is a form of energy produced by vibrating objects and transmitted through a medium.

Q2. Why cannot sound travel through a vacuum?

Answer: Sound requires a material medium to travel. Since a vacuum has no particles, sound cannot propagate through it.

Q3. Define frequency.

Answer: Frequency is the number of vibrations produced in one second.

Q4. What is amplitude?

Answer: Amplitude is the maximum displacement of particles from their mean position.

Complete Class 9 Maths NCERT Solutions | Ganita Manjari Part 1 PDF: Download Now

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Q5. What is wavelength?

Answer: Wavelength is the distance between two consecutive compressions or rarefactions.

Q6. What is an echo?

Answer: Echo is the repetition of sound due to reflection from a distant surface.

Q7. What are ultrasonic waves?

Answer: Ultrasonic waves are sound waves having frequencies greater than 20,000 Hz.

Multiple Choice Questions (MCQs)

1. Sound is produced by:

A. Light
B. Heat
C. Vibrations
D. Electricity

Answer: Vibrations

2. SI unit of frequency is:

A. Newton
B. Joule
C. Hertz
D. Watt

Answer: Hertz

3. Sound cannot travel through:

A. Solids
B. Liquids
C. Gases
D. Vacuum

Answer: Vacuum

4. Loudness depends on:

A. Frequency
B. Amplitude
C. Speed
D. Wavelength

Answer: Amplitude

5. Ultrasonic waves have frequency greater than:

A. 20 Hz
B. 200 Hz
C. 2000 Hz
D. 20,000 Hz

Answer: 20,000 Hz

Exam Preparation Tips

• Learn definitions of amplitude, frequency, wavelength, and pitch.

• Understand the difference between loudness and pitch.

• Practice numerical problems based on sound waves.

• Revise applications of ultrasonic waves and SONAR.

• Solve NCERT questions and MCQs regularly.

Key Takeaways

• Sound is produced by vibrations.

• Sound travels through solids, liquids, and gases.

• Sound cannot travel in a vacuum.

• Frequency determines pitch.

• Amplitude determines loudness.

• Echo is caused by reflection of sound.

• Ultrasonic waves have numerous practical applications.

Complete Class 9 Maths NCERT Solutions | Ganita Manjari Part 1 PDF: Download Now

NCERT Solutions for Class 9 Science (New Book) – Chapter-wise PDF: Download Now

Conclusion

The chapter Sound Waves: Characteristics and Applications helps students understand the nature of sound and its importance in everyday life. Concepts such as amplitude, frequency, wavelength, echo, and ultrasonic waves are essential for understanding Physics and various modern technologies. Thorough preparation of NCERT questions and concepts will help students excel in examinations and develop a strong scientific foundation.