ICSE Class 10 Physics: Sound — Important Questions with Answers 2026

Short Answer Questions (2-3 Marks)

• Q: What is sound? How is it produced?
  Ans: Sound is a form of energy that produces the sensation of hearing. It is produced by vibrating bodies. When an object vibrates, it creates compressions and rarefactions in the surrounding medium, forming a longitudinal wave that carries the sound energy.
• Q: Differentiate between longitudinal waves and transverse waves.
  Ans: Longitudinal waves: particles vibrate parallel to the direction of wave propagation, consist of compressions and rarefactions. Example: sound waves. Transverse waves: particles vibrate perpendicular to the direction of wave propagation, consist of crests and troughs. Example: light waves, water waves.
• Q: Define: (i) Frequency, (ii) Wavelength, (iii) Amplitude of a sound wave.
  Ans: (i) Frequency: Number of vibrations per second. Unit: Hertz (Hz). (ii) Wavelength (λ): Distance between two consecutive compressions or rarefactions. Unit: metre. (iii) Amplitude: Maximum displacement of a particle from its mean position. It determines the loudness of sound.
• Q: State the relation between speed, frequency and wavelength.
  Ans: v = f × λ (speed = frequency × wavelength). Speed of sound in air at 20°C is approximately 343 m/s. Speed increases with temperature and is highest in solids, lower in liquids, and lowest in gases.
• Q: What are the characteristics of sound? How does pitch differ from loudness?
  Ans: Characteristics: (1) Loudness — depends on amplitude and area of vibrating body. (2) Pitch — depends on frequency; higher frequency means higher pitch. (3) Quality/Timbre — depends on waveform; distinguishes between same note played by different instruments.

Long Answer / Application Questions (4-6 Marks)

• Q: What is an echo? State two conditions for hearing an echo.
  Ans: An echo is the repetition of sound caused by reflection from a hard surface. Conditions: (1) The minimum distance between source and reflecting surface should be 17.2 m (at 20°C) so that the reflected sound reaches the ear after 0.1 s. (2) The reflecting surface should be large and hard.
• Q: The speed of sound in air is 340 m/s. A person claps near a cliff and hears the echo after 3 seconds. Find the distance of the cliff.
  Ans: Time for echo = 2d/v (sound travels to cliff and back). 3 = 2d/340. d = (3 × 340)/2 = 510 m. The cliff is 510 m away.
• Q: Explain the use of ultrasound in medical diagnosis.
  Ans: Ultrasound (frequency > 20,000 Hz) is used in: (1) Sonography/Ultrasonography — imaging internal organs, monitoring fetal development during pregnancy. (2) Echocardiography — imaging the heart. (3) Lithotripsy — breaking kidney stones using focused ultrasound waves. (4) Cleaning — industrial cleaning of precision parts.

Exam Tips for This Chapter

• Revise all definitions and laws from Sound — they are commonly asked as 1-2 mark questions
• Practice diagrams related to Sound — neat labelled diagrams carry 2-3 marks
• For numericals, always show formula → substitution → answer with correct units
• Previous year analysis shows Sound carries 8-12 marks in the board exam