Worksheet Solutions: Sound | Physics Class 10 ICSE PDF Download

Part A — Multiple Choice Questions 

Q1. Which type of sound wave has frequency higher than 20,000 hertz?

• (a) Infrasonic waves

• (b) Ultrasonic waves

• (c) Audible waves

• (d) Transverse waves

Answer: (b) Ultrasonic waves
Explanation: Sounds above 20,000 hertz cannot be heard by human ears and are called ultrasonic.

Q2. Sound cannot travel through:

• (a) Air

• (b) Water

• (c) Vacuum

• (d) Steel

Answer: (c) Vacuum
Explanation: Sound is a mechanical wave, it requires a medium like air, water, or solids to travel. It cannot pass through vacuum.

Q3. Which one is the correct relation between wave velocity (V), frequency (f), and wavelength (λ)?

• (a) V = f + λ

• (b) V = f ÷ λ

• (c) V = f × λ

• (d) V = λ ÷ f

Answer: (c) V = f × λ

Q4. The repetition of sound due to reflection from a surface is called:

• (a) Refraction

• (b) Echo

• (c) Resonance

• (d) Diffraction

Answer: (b) Echo

Q5. Loudness of sound mainly depends on:

• (a) Frequency of sound

• (b) Amplitude of vibration

• (c) Wavelength of sound

• (d) Speed of sound

Answer: (b) Amplitude of vibration

Part B — Short Answer Questions 

Q6. What is the difference between infrasonic, audible and ultrasonic sounds?
Answer:

• Infrasonic: Sounds below 20 hertz, not heard by humans.

• Audible: Sounds between 20 hertz and 20,000 hertz, heard by humans.

• Ultrasonic: Sounds above 20,000 hertz, not heard by humans.

Q7. What are longitudinal waves? Give one example in daily life.
Answer:
In longitudinal waves, particles of the medium vibrate in the same direction as the wave travels. They consist of compressions and rarefactions.
Example: Sound waves in air are longitudinal waves.

Q8. State the condition required to hear a distinct echo.
Answer:
For a distinct echo, the time gap between the original sound and reflected sound must be at least 0.1 second. Since sound travels about 340 metres per second in air, the obstacle should be at least 17 metres away.

Q9. What is resonance? Give one example.
Answer:
Resonance happens when the frequency of an external force matches the natural frequency of a body, causing large vibrations.
Example: When one tuning fork is struck, another fork of the same frequency nearby also starts vibrating loudly due to resonance.

Q10. How can dolphins or fishermen use ultrasonic sound?
Answer:

• Dolphins emit ultrasonic waves and detect echoes to locate prey or obstacles.

• Fishermen use ultrasonic pulses in sonar systems to detect shoals of fish under water.

Part C — Long Answer Questions 

Q11.  A boy shouts near a tall wall and hears the echo after 0.5 seconds. If the speed of sound in air is 340 metres per second, find the distance of the wall from the boy.
Solution:

• Time taken for sound to travel to the wall and back = 0.5 seconds.

• Distance travelled = speed × time = 340 × 0.5 = 170 metres.

• Since this is the to-and-fro distance, distance of wall = 170 ÷ 2 = 85 metres.
  Answer: The wall is 85 metres away.

Q12. Explain the differences between free vibrations, damped vibrations and forced vibrations with one example of each.
Solution:

• Free vibrations: Vibrations without any external force, amplitude remains constant in ideal case.
  Example: A pendulum oscillating in vacuum.

• Damped vibrations: Vibrations with decreasing amplitude due to resistive forces like air.
  Example: A tuning fork vibrating in air.

• Forced vibrations: Vibrations produced under influence of an external periodic force.
  Example: Vibrations of air inside the sound box of a guitar.
  Answer: Free vibrations occur naturally, damped vibrations fade due to resistance, and forced vibrations are maintained by external force.

Q13.  A simple pendulum swings back and forth producing sound. Explain how energy changes during its motion.
Solution:

1. At extreme positions, the pendulum has maximum potential energy and no kinetic energy.

2. As it moves towards mean position, potential energy changes into kinetic energy.

3. At mean position, the pendulum has maximum kinetic energy and no potential energy.

4. As it moves to the other extreme, kinetic energy again changes into potential energy.

5. Total energy remains constant but changes form during motion.
   Answer: The pendulum shows the conservation of energy principle, similar to how sound-producing bodies convert energy between potential and kinetic forms.