💡 Print paper or share solutions as PDF via WhatsApp to students.
CHAPTER 10 — SOUND
Class IX Science — Sound Waves
Preeti Kushwah Classes — Unit Test (Set 1: Foundation)
General Instructions:
1. All questions are compulsory.
2. Section A has 6 questions of 1 mark each.
3. Section B has 5 questions of 2 marks each.
4. Section C has 4 questions of 3 marks each.
5. Section D has 2 questions of 5 marks each.
6. Draw neat diagrams wherever required. Show all steps in numerical problems.
1. All questions are compulsory.
2. Section A has 6 questions of 1 mark each.
3. Section B has 5 questions of 2 marks each.
4. Section C has 4 questions of 3 marks each.
5. Section D has 2 questions of 5 marks each.
6. Draw neat diagrams wherever required. Show all steps in numerical problems.
Section A — (1 Mark Each) [6 × 1 = 6]
Q1.1
Sound is produced by ___ objects. (Fill in the blank)
Q2.1
What is the SI unit of frequency?
Q3.1
True or False: Sound can travel through vacuum.
Q4.1
Name the characteristic of sound that depends on amplitude.
Q5.1
What is the audible range of the average human ear?
Q6.1
What does SONAR stand for?
Section B — (2 Marks Each) [5 × 2 = 10]
Q7.2
Define compression and rarefaction in a sound wave.
Q8.2
Why are sound waves called mechanical waves?
Q9.2
A sound wave has frequency 200 Hz. Calculate its time period.
Q10.2
What is an echo? What is the minimum distance required to hear an echo at 20°C?
Q11.2
List any two applications of ultrasound with brief explanation.
Section C — (3 Marks Each) [4 × 3 = 12]
Q12.3
Draw a neat diagram showing compressions and rarefactions in a sound wave produced by a vibrating tuning fork. Define wavelength and amplitude.
Q13.3
Differentiate between longitudinal and transverse waves. (Give at least 3 differences in tabular form)
Q14.3
A person claps his hands near a cliff and hears the echo after 3 seconds. If the speed of sound in air is 344 m/s, calculate the distance of the cliff from the person.
Q15.3
Describe the bell jar experiment with a diagram. What does it demonstrate?
Section D — (5 Marks Each) [2 × 5 = 10]
Q16.5
(a) Name the three characteristics of sound and state what each depends on. [3]
(b) A girl is playing on a swing near a building. She hears the echo of her clap after 1 s. If speed of sound is 340 m/s, how far is the building from the swing? [2]
(b) A girl is playing on a swing near a building. She hears the echo of her clap after 1 s. If speed of sound is 340 m/s, how far is the building from the swing? [2]
Q17.5
(a) Describe the working of SONAR with a neat diagram. [3]
(b) A submarine sends a sonar pulse which returns from an underwater cliff in 1.02 s. If speed of sound in salt water is 1531 m/s, how far is the cliff? [2]
(b) A submarine sends a sonar pulse which returns from an underwater cliff in 1.02 s. If speed of sound in salt water is 1531 m/s, how far is the cliff? [2]
Bonus Question (Optional) [2 Marks]
Q18.2
★ Why does sound travel fastest in solids and slowest in gases? Explain with an example.
Preeti Kushwah Classes
Scan for more notes & papers
www.preetikushwahclasses.com
Scan for more notes & papers
www.preetikushwahclasses.com
Answer Key & Detailed Solutions
Q1. [1 Mark]
Vibrating. Sound is produced by vibrating objects.
Q2. [1 Mark]
Hertz (Hz). One hertz equals one vibration per second.
Q3. [1 Mark]
False. Sound needs a material medium; it cannot travel through vacuum.
Q4. [1 Mark]
Loudness. The loudness of a sound depends on the amplitude of the vibration.
Q5. [1 Mark]
20 Hz to 20,000 Hz (20 kHz).
Q6. [1 Mark]
Sound Navigation And Ranging.
Q7. [2 Marks]
Compression: A region of high pressure where particles are pushed close together. [1 mark]
Rarefaction: A region of low pressure where particles are spread apart. [1 mark]
Together they form a longitudinal wave.
Rarefaction: A region of low pressure where particles are spread apart. [1 mark]
Together they form a longitudinal wave.
Q8. [2 Marks]
Sound waves need a material medium (solid, liquid, or gas) for propagation. [1 mark]
They cannot travel through vacuum. Hence they are called mechanical waves. [1 mark]
They cannot travel through vacuum. Hence they are called mechanical waves. [1 mark]
Q9. [2 Marks]
Time period T = 1 ÷ f [1 mark]
T = 1 ÷ 200 = 0.005 s [1 mark]
T = 1 ÷ 200 = 0.005 s [1 mark]
Q10. [2 Marks]
Echo is the repetition of sound caused by reflection from a hard surface. [1 mark]
Minimum distance = v × t ÷ 2 = 344 × 0.1 ÷ 2 = 17.2 m (at 20°C). [1 mark]
Minimum distance = v × t ÷ 2 = 344 × 0.1 ÷ 2 = 17.2 m (at 20°C). [1 mark]
Q11. [2 Marks]
(i) Medical imaging (ultrasonography): Used to get images of internal organs and examine foetus during pregnancy. [1 mark]
(ii) Cleaning: Ultrasonic waves dislodge dirt from hard-to-reach parts of jewellery and electronic components. [1 mark]
(ii) Cleaning: Ultrasonic waves dislodge dirt from hard-to-reach parts of jewellery and electronic components. [1 mark]
Q12. [3 Marks]
[Diagram showing alternating C–R–C–R pattern from tuning fork] [1 mark]
Wavelength (λ): The distance between two consecutive compressions or two consecutive rarefactions. [1 mark]
Amplitude (A): The maximum displacement of particles from their mean (equilibrium) position. [1 mark]
Wavelength (λ): The distance between two consecutive compressions or two consecutive rarefactions. [1 mark]
Amplitude (A): The maximum displacement of particles from their mean (equilibrium) position. [1 mark]
Q13. [3 Marks]
| Property | Longitudinal Wave | Transverse Wave |
|---|---|---|
| Particle vibration | Parallel to wave direction | Perpendicular to wave direction |
| Regions formed | Compressions & rarefactions | Crests & troughs |
| Medium requirement | Needs a medium (e.g., sound in air) | Does not always need a medium (e.g., light waves) |
Q14. [3 Marks]
Given: t = 3 s, v = 344 m/s [½ mark]
Total distance = v × t = 344 × 3 = 1032 m [1 mark]
Distance of cliff = Total distance ÷ 2 = 1032 ÷ 2 = 516 m [1 mark]
The cliff is 516 m away from the person. [½ mark]
Total distance = v × t = 344 × 3 = 1032 m [1 mark]
Distance of cliff = Total distance ÷ 2 = 1032 ÷ 2 = 516 m [1 mark]
The cliff is 516 m away from the person. [½ mark]
Q15. [3 Marks]
An electric bell is placed inside a bell jar connected to a vacuum pump. [½ mark]
When air is pumped out gradually, the sound becomes fainter and fainter. [1 mark]
In complete vacuum, no sound is heard even though the bell is still vibrating (visible). [½ mark]
When air is let back in, the sound returns. [½ mark]
This demonstrates that sound needs a material medium for propagation. [½ mark]
[Diagram: Bell jar with bell, vacuum pump, battery shown]
When air is pumped out gradually, the sound becomes fainter and fainter. [1 mark]
In complete vacuum, no sound is heard even though the bell is still vibrating (visible). [½ mark]
When air is let back in, the sound returns. [½ mark]
This demonstrates that sound needs a material medium for propagation. [½ mark]
[Diagram: Bell jar with bell, vacuum pump, battery shown]
Q16. [5 Marks]
(a) Three characteristics of sound: [3 marks]
• Pitch — depends on frequency. [1 mark]
• Loudness — depends on amplitude. [1 mark]
• Quality / Timbre — depends on waveform. [1 mark]
(b) Given: t = 1 s, v = 340 m/s [2 marks]
Distance = v × t ÷ 2 = 340 × 1 ÷ 2 = 170 m.
The building is 170 m away from the swing.
• Pitch — depends on frequency. [1 mark]
• Loudness — depends on amplitude. [1 mark]
• Quality / Timbre — depends on waveform. [1 mark]
(b) Given: t = 1 s, v = 340 m/s [2 marks]
Distance = v × t ÷ 2 = 340 × 1 ÷ 2 = 170 m.
The building is 170 m away from the swing.
Q17. [5 Marks]
(a) Working of SONAR: [3 marks]
• A transmitter on the ship sends ultrasonic pulses towards the ocean floor. [1 mark]
• The pulses reflect off underwater objects/floor and return to the receiver on the ship. [1 mark]
• The time taken for the return trip is used to calculate depth using d = v × t ÷ 2. [1 mark]
[Neat diagram: Ship on surface, transmitter sends pulse down, pulse reflects off ocean floor, receiver detects echo]
(b) Given: t = 1.02 s, v = 1531 m/s [2 marks]
d = v × t ÷ 2 = 1531 × 1.02 ÷ 2
d = 1561.62 ÷ 2 = 780.81 m.
The cliff is 780.81 m away from the submarine.
• A transmitter on the ship sends ultrasonic pulses towards the ocean floor. [1 mark]
• The pulses reflect off underwater objects/floor and return to the receiver on the ship. [1 mark]
• The time taken for the return trip is used to calculate depth using d = v × t ÷ 2. [1 mark]
[Neat diagram: Ship on surface, transmitter sends pulse down, pulse reflects off ocean floor, receiver detects echo]
(b) Given: t = 1.02 s, v = 1531 m/s [2 marks]
d = v × t ÷ 2 = 1531 × 1.02 ÷ 2
d = 1561.62 ÷ 2 = 780.81 m.
The cliff is 780.81 m away from the submarine.
Q18. Bonus [2 Marks]
In solids, particles are closely packed and strongly bonded — vibrations transmit very quickly (e.g., iron: 5130 m/s). [½ mark]
In liquids, particles are less closely packed (e.g., water: 1498 m/s). [½ mark]
In gases, particles are far apart with weak intermolecular forces (e.g., air: 344 m/s). [½ mark]
So the speed order is: Solid > Liquid > Gas. [½ mark]
In liquids, particles are less closely packed (e.g., water: 1498 m/s). [½ mark]
In gases, particles are far apart with weak intermolecular forces (e.g., air: 344 m/s). [½ mark]
So the speed order is: Solid > Liquid > Gas. [½ mark]