Chapter: 10 – Sound Waves: Characteristics and Applications
Maximum Marks: 50
Suggested Time: 1 Hour 30 Minutes

This Class 9 Science Exploration Chapter 10 Sample Paper 1 is designed to help students practise important concepts from “Sound Waves: Characteristics and Applications.” The paper covers production and propagation of sound, sound waves, vibrations, amplitude, frequency, time period, wavelength, speed of sound, loudness, pitch, echo, ultrasound, infrasound, and applications of sound. Complete solutions are provided at the end.

Sample Paper 1

General Instructions

1. All questions are compulsory.
2. Read each question carefully.
3. Show all steps in numerical questions.
4. Write appropriate SI units wherever required.
5. Draw neat and labelled diagrams wherever necessary.
6. Use the formulae given in the question when required.

Section A — Objective Questions

10 × 1 = 10 Marks

Q1. Sound is produced by:

a) Light
b) Vibrating objects
c) Stationary objects
d) Magnetic fields

Q2. Sound needs a ________ for its propagation.

a) Vacuum
b) Material medium
c) Light source
d) Electric field

Q3. The number of vibrations made by an object per second is called:

a) Amplitude
b) Wavelength
c) Frequency
d) Time period

Q4. The SI unit of frequency is:

a) Metre
b) Second
c) Hertz
d) Decibel

Q5. The maximum displacement of a vibrating particle from its mean position is called:

a) Frequency
b) Amplitude
c) Wavelength
d) Time period

Q6. The characteristic of sound mainly related to frequency is:

a) Loudness
b) Pitch
c) Quality
d) Intensity

Q7. A sound with a higher frequency has:

a) Lower pitch
b) Higher pitch
c) Lower amplitude only
d) No pitch

Q8. Which type of sound has a frequency greater than 20,000 Hz?

a) Infrasound
b) Audible sound
c) Ultrasound
d) Normal sound

Q9. The repetition of sound caused by reflection from a distant surface is called:

a) Refraction
b) Echo
c) Diffraction
d) Absorption

Q10. Which of the following is an application of ultrasound?

a) Medical imaging
b) Making shadows
c) Producing sunlight
d) Measuring temperature only

Section B — Very Short Answer Questions

5 × 2 = 10 Marks

Q11. What is sound? How is it produced?

Q12. Define frequency and amplitude of a sound wave.

Q13. Differentiate between loudness and pitch.

Q14. What is an echo? State one condition necessary for hearing a distinct echo.

Q15. What are ultrasound and infrasound?

Section C — Short Answer and Numerical Questions

4 × 3 = 12 Marks

Q16. Explain why sound cannot travel through a vacuum.

Q17. A sound source vibrates 500 times in 2 seconds. Calculate its frequency.

Q18. A sound wave has a frequency of 250 Hz. Calculate its time period.

Q19. Explain how amplitude and frequency affect the characteristics of sound.

Section D — Application-Based and Numerical Questions

2 × 4 = 8 Marks

Q20. A sound wave travels with a speed of 340 m/s and has a frequency of 170 Hz.

Calculate:

a) The wavelength of the sound wave.
b) The frequency of the wave.
c) What happens to wavelength if the frequency is doubled while speed remains constant?
d) Write the relation between wave speed, frequency and wavelength.

Q21. A student strikes two tuning forks. Tuning fork A has a frequency of 256 Hz, while tuning fork B has a frequency of 512 Hz.

Answer the following:

a) Which tuning fork produces the higher-pitched sound?
b) Why?
c) Which tuning fork completes more vibrations per second?
d) Will frequency alone determine which sound is louder?

Section E — Long Answer and Numerical Questions

2 × 5 = 10 Marks

Q22. Explain the main characteristics of a sound wave. Discuss amplitude, frequency, time period and wavelength. Also explain how frequency and amplitude influence the sound we hear.

Q23. A student stands 170 m away from a large wall and shouts. The speed of sound in air is 340 m/s.

Calculate:

a) The distance travelled by the sound from the student to the wall and back.
b) The time taken for the echo to return.
c) What phenomenon produces the echo?
d) Why is a large, hard surface suitable for producing an echo?
e) What happens if the reflecting surface absorbs most of the sound?

SOLUTIONS

Section A — Answers

Q1. b) Vibrating objects

Q2. b) Material medium

Q3. c) Frequency

Q4. c) Hertz

Q5. b) Amplitude

Q6. b) Pitch

Q7. b) Higher pitch

Q8. c) Ultrasound

Q9. b) Echo

Q10. a) Medical imaging

Section B — Solutions

Q11. Sound

Sound is a form of energy that produces the sensation of hearing.

Sound is generally produced when an object vibrates.

For example, when a tuning fork vibrates, it causes the surrounding medium to vibrate, producing sound.

Q12. Frequency and Amplitude

Frequency is the number of complete vibrations made by a vibrating object in one second.

Its SI unit is:Hertz (Hz)​

Amplitude is the maximum displacement of a vibrating particle from its mean position.

Amplitude is related to the strength or loudness of a sound.

Q13. Loudness and Pitch

Q14. Echo

An echo is a repetition of sound heard after the sound is reflected from a distant surface.

For a distinct echo, the reflected sound should reach the listener after a sufficient time interval from the original sound.

A sufficiently large and hard reflecting surface and adequate distance between the source and reflector help produce a distinct echo.

Q15. Ultrasound and Infrasound

Ultrasound: Sound having a frequency greater than 20,000 Hz.f>20,000 Hz​

Infrasound: Sound having a frequency below 20 Hz.f<20 Hz​

Humans generally cannot hear either range.

Section C — Solutions

Q16. Sound Cannot Travel Through a Vacuum

Sound is a mechanical wave. It travels by causing particles of a material medium to vibrate and transfer energy from one particle to another.

A vacuum has no particles.

Therefore, there are no particles available to transmit the vibrations.

Hence:Sound cannot travel through a vacuum.​

Q17. Frequency

Given:

Number of vibrations:N=500

Time:t=2 s

Frequency is:f=tN​

Therefore:f=2500​f=250 Hz​

Answer: The frequency is 250 Hz.

Q18. Time Period

Given:f=250 Hz

The relation between frequency and time period is:T=f1​

Therefore:T=2501​T=0.004 sT=0.004 s​

orT=4 ms​

Q19. Amplitude and Frequency

Amplitude affects the strength or loudness of sound.

• Greater amplitude → generally louder sound.
• Smaller amplitude → generally softer sound.

Frequency affects the pitch of sound.

• Higher frequency → higher-pitched sound.
• Lower frequency → lower-pitched sound.

Thus, amplitude and frequency affect different characteristics of sound.

Section D — Solutions

Q20. Wavelength

Given:

Speed:v=340 m/s

Frequency:f=170 Hz

The relation is:v=fλ

Therefore:λ=fv​λ=170340​λ=2 m​

a) Wavelength

2 m​

b) Frequency

Given:170 Hz​

c) If frequency is doubled

If speed remains constant:v=fλ

Therefore, wavelength is inversely proportional to frequency.

If frequency doubles, wavelength becomes half.

Original wavelength:2 m

New wavelength:1 m​

d) Wave relation

v=fλ​

Q21. Comparing Two Tuning Forks

Given:

Tuning fork A:fA​=256 Hz

Tuning fork B:fB​=512 Hz

a) Higher-pitched sound

Tuning fork B produces the higher-pitched sound.Tuning fork B​

b) Reason

Pitch depends mainly on frequency.

Since:512>256

tuning fork B has the higher frequency and therefore produces the higher pitch.

c) More vibrations per second

Tuning fork B completes more vibrations per second.

• A = 256 vibrations/s
• B = 512 vibrations/s

d) Does frequency determine loudness?

No.

Frequency mainly determines pitch, while amplitude is more closely related to loudness.

Therefore, frequency alone does not determine which sound is louder.

Section E — Solutions

Q22. Characteristics of Sound Waves

Important characteristics of a sound wave include amplitude, frequency, time period and wavelength.

1. Amplitude

Amplitude is the maximum displacement of a vibrating particle from its mean position.

Greater amplitude generally produces a louder sound, while smaller amplitude produces a softer sound.

2. Frequency

Frequency is the number of complete vibrations made per second.

Its SI unit is Hertz (Hz).

Higher frequency produces a higher-pitched sound, while lower frequency produces a lower-pitched sound.

3. Time Period

Time period is the time taken to complete one vibration.

It is related to frequency by:T=f1​

4. Wavelength

Wavelength is the distance between two successive points in the wave that are in the same phase, such as two successive compressions or rarefactions in a longitudinal sound wave.

The relation between speed, frequency and wavelength is:v=fλ

Summary

Q23. Echo Calculation

Given:

Distance between student and wall:d=170 m

Speed of sound:v=340 m/s

a) Total distance travelled

The sound travels from the student to the wall and then returns.

Therefore:Total distance=2d=2×170340 m​

b) Time taken for echo

Using:v=ts​

Therefore:t=vs​t=340340​t=1 s​

Thus, the echo returns after 1 second.

c) Phenomenon producing echo

An echo is produced by the reflection of sound from a suitable reflecting surface.

d) Suitable reflecting surface

A large, hard surface is suitable because it reflects a significant amount of sound.

Examples include large walls, cliffs and buildings.

e) If the surface absorbs most of the sound

If the surface absorbs most of the sound, very little sound is reflected back.

Therefore, the echo will be weak or may not be clearly heard.

Final Answers

• Total distance = 340 m
• Echo time = 1 s
• Phenomenon = Reflection of sound
• Large hard surfaces provide strong reflection
• Sound-absorbing surfaces reduce or weaken echoes