๐น Very Short Answer (1 mark)
Q1. What is sound?
Ans. Vibrations that travel through a medium and can be heard by our ears.
Q2. Name the medium through which sound cannot travel.
Ans. Vacuum (no air or particles).
Q3. What is amplitude of a sound wave?
Ans. Maximum displacement of particles from mean position.
Q4. What is wavelength?
Ans. Distance between two successive compressions or rarefactions.
Q5. What is frequency of sound?
Ans. Number of vibrations per second (measured in Hz).
Q6. What is pitch?
Ans. Highness or lowness of a sound determined by frequency.
Q7. What is loudness?
Ans. Perception of intensity of sound by our ears.
Q8. What is echo?
Ans. Reflection of sound which can be heard after a delay.
Q9. Speed of sound in air at 0ยฐC?
Ans. 331 m/s.
Q10. Speed of sound in solids, liquids, gases?
Ans. Solids > Liquids > Gases (because of particle density and elasticity).
๐น Short Answer (2โ3 marks)
Q11. Define ultrasonics.
Ans. Sounds with frequency above 20,000 Hz (inaudible to humans).
Q12. Define infrasonics.
Ans. Sounds with frequency below 20 Hz.
Q13. Define audibility range for humans.
Ans. 20 Hz โ 20,000 Hz.
Q14. What is reverberation?
Ans. Persistence of sound in a hall due to repeated reflections.
Q15. Give one application of ultrasonics.
Ans. Medical imaging (ultrasound).
Q16. Give one application of infrasonics.
Ans. Detect earthquakes, volcanic activity.
Q17. Define natural frequency.
Ans. The frequency at which a body naturally vibrates when disturbed.
Q18. What is resonance?
Ans. When a body vibrates with maximum amplitude at its natural frequency due to another vibrating body.
Q19. Define time period of sound wave.
Ans. Time taken for one complete vibration.
Q20. Define compression and rarefaction.
Ans.
- Compression: region of high pressure in a sound wave.
- Rarefaction: region of low pressure.
๐น Long Answer (4โ5 marks)
Q21. Difference between loudness and intensity.
| Loudness | Intensity |
|---|---|
| Perceived by ear | Energy transmitted per sec per unit area |
| Subjective | Objective |
| Depends on amplitude | Depends on energy |
Q22. Difference between pitch and frequency.
| Pitch | Frequency |
|---|---|
| Perception of sound | Physical quantity (Hz) |
| Subjective | Objective |
| High pitch โ high frequency | Measured in Hz |
Q23. Explain the reflection of sound.
Ans. When sound waves strike a surface and bounce back, it is reflection of sound โ produces echo or reverberation.
Q24. Conditions for echo.
Ans.
- Sound must be loud enough.
- Distance of reflecting surface โฅ 17 m.
- Minimum time interval between original and reflected sound = 0.1 s.
Q25. Difference between echo and reverberation.
| Echo | Reverberation |
|---|---|
| Single reflected sound | Continuous reflected sounds |
| Heard separately | Merges with original sound |
| Distance > 17 m | Short distance |
Q26. Explain speed of sound in different media.
Ans. Solids > Liquids > Gases because particles are closer โ transmit vibrations faster.
Q27. Explain production of sound.
Ans. Produced by vibrating objects โ transmitted by medium โ reaches ear โ perceived.
Q28. Explain working of human ear.
Ans. Sound vibrations โ ear canal โ eardrum vibrates โ ossicles amplify โ cochlea converts to nerve impulses โ brain.
Q29. Explain Doppler effect.
Ans. Apparent change in frequency of sound due to relative motion between source and observer.
Q30. Give two examples of Doppler effect.
Ans. Ambulance siren approaching/going away, moving train whistle.
๐น Case Study / Application-Based (5โ6 marks)
Q31. Case Study โ Echo
A person shouts in valley โ echo heard after 0.5 s.
(i) What is echo?
(ii) Why does it occur?
Ans.
(i) Reflection of sound.
(ii) Sound waves bounce from hill surfaces back to listener.
Q32. Case Study โ Ultrasound
Ultrasonics used in medical imaging.
(i) Why ultrasonics used?
Ans. High frequency โ small wavelength โ precise imaging.
Q33. Why does a drum produce sound when struck?
Ans. Membrane vibrates โ air vibrates โ sound waves propagate.
Q34. Case Study โ Bat using sound
Bats use ultrasound to detect obstacles โ echo returns โ bat identifies distance and object.
Q35. Why do we hear thunder after lightning?
Ans. Light travels faster โ sound slower โ delay โ thunder.
Q36. Case Study โ Submarine sonar
Submarines use ultrasonics โ echoes from sea floor โ detect objects โ navigation and mapping.
Q37. Why does sound become faint in longer hall without proper acoustics?
Ans. Energy dissipated โ multiple reflections โ weak intensity โ reverberation needed.
Q38. Why do high-pitched sounds travel shorter distances than low-pitched?
Ans. High frequency โ more absorption by air โ energy dissipates faster.
Q39. Why can sound travel in solids better than in air?
Ans. Particles closer โ vibrations transmitted faster โ higher speed and efficiency.
Q40. Why is vacuum silent?
Ans. No medium โ no particle vibration โ sound cannot propagate.
๐น Extra Important (41โ50)
Q41. Define amplitude of sound.
Ans. Maximum displacement of particle from mean โ determines loudness.
Q42. Define frequency of sound.
Ans. Number of vibrations per second โ determines pitch.
Q43. Relation between frequency and pitch.
Ans. Higher frequency โ higher pitch.
Q44. What is audible range for humans?
Ans. 20 Hz โ 20,000 Hz.
Q45. What is ultrasound?
Ans. Sound above 20 kHz, inaudible to humans.
Q46. What is infrasound?
Ans. Sound below 20 Hz, inaudible to humans.
Q47. Give two uses of ultrasound.
Ans. Medical imaging, cleaning jewelry, sonar detection.
Q48. Give two uses of infrasound.
Ans. Earthquake detection, volcanic eruption monitoring.
Q49. What is sonic boom?
Ans. Loud sound produced when an object exceeds speed of sound.
Q50. Why do musical instruments produce different sounds?
Ans. Due to differences in shape, length, tension, and material โ different frequencies and timbre.