Sound Part 3: MCQs (Q51–Q75)
🎵 Sound – Class 9 Science MCQs
Section 3: Reflection of Sound, Echo, Reverberation & Applications (Q51–Q75)
Q51. Reflection of sound is governed by:
A. Laws of refraction
B. Laws of reflection
C. Newton’s laws
D. Kepler’s laws
✅ Correct Answer: B. Laws of reflection
Explanation:
- Sound obeys same reflection laws as light → angle of incidence = angle of reflection.
Q52. Which of these is an application of reflection of sound?
A. Echo
B. SONAR
C. Megaphones
D. All of these
✅ Correct Answer: D. All of these
Q53. Time gap between original sound and echo must be at least:
A. 0.01 s
B. 0.05 s
C. 0.1 s
D. 1 s
✅ Correct Answer: C. 0.1 s
Explanation:
- Human ear can distinguish two sounds if interval ≥ 0.1 s.
Q54. If speed of sound is 340 m/s, minimum distance for echo = ?
A. 8.5 m
B. 17 m
C. 34 m
D. 68 m
✅ Correct Answer: B. 17 m
Explanation:
- Distance = v × t/2 = 340 × 0.1/2 = 17 m.
Q55. Multiple reflections of sound cause:
A. Echo
B. Reverberation
C. Refraction
D. Diffraction
✅ Correct Answer: B. Reverberation
Q56. Reverberation occurs mostly in:
A. Open fields
B. Large halls and auditoriums
C. Small rooms
D. Open sky
✅ Correct Answer: B. Large halls and auditoriums
Q57. Reverberation can be reduced by:
A. Increasing echoes
B. Using sound-absorbing materials
C. Using more loudspeakers
D. None
✅ Correct Answer: B. Using sound-absorbing materials
Explanation:
- Materials like curtains, carpets, and acoustic panels absorb sound.
Q58. Which device uses multiple reflection of sound?
A. Megaphone
B. Trumpet
C. Stethoscope
D. All of these
✅ Correct Answer: D. All of these
Q59. Megaphones work on principle of:
A. Refraction
B. Reflection of sound
C. Diffraction
D. Dispersion
✅ Correct Answer: B. Reflection of sound
Q60. The device used by doctors to hear patient’s heartbeat is:
A. Megaphone
B. Microphone
C. Stethoscope
D. Loudspeaker
✅ Correct Answer: C. Stethoscope
Explanation:
- Works on multiple reflection of sound in tubes.
Q61. Sound waves obey:
A. Reflection only
B. Refraction only
C. Both reflection and refraction
D. Neither
✅ Correct Answer: C. Both reflection and refraction
Q62. Echoes are used by which animals for navigation?
A. Dogs
B. Bats
C. Lions
D. Cows
✅ Correct Answer: B. Bats
Q63. SONAR is based on:
A. Reflection of sound
B. Refraction of sound
C. Diffraction of sound
D. Absorption of sound
✅ Correct Answer: A. Reflection of sound
Q64. Full form of SONAR is:
A. Sound Navigation and Ranging
B. Sound Notation and Recording
C. Sound Neutralisation and Reflection
D. Sound Noise and Radiation
✅ Correct Answer: A. Sound Navigation and Ranging
Q65. SONAR is used to measure:
A. Height of building
B. Depth of sea
C. Speed of light
D. Frequency of radio
✅ Correct Answer: B. Depth of sea
Q66. Echocardiography is used for:
A. Scanning brain
B. Studying heart
C. Hearing aids
D. Detecting metal cracks
✅ Correct Answer: B. Studying heart
Q67. Ultrasonography is used for:
A. Detecting underwater objects
B. Imaging internal body organs
C. Amplifying sound
D. Making sound louder
✅ Correct Answer: B. Imaging internal body organs
Q68. Ultrasonic waves are used to clean:
A. Clothes
B. Delicate parts like watches and machines
C. Hands
D. Walls
✅ Correct Answer: B. Delicate parts like watches and machines
Q69. Bats avoid obstacles at night using:
A. Light
B. Infrasonic waves
C. Echolocation
D. Heat vision
✅ Correct Answer: C. Echolocation
Q70. Multiple echoes are called:
A. Reverberation
B. Resonance
C. Beats
D. Diffraction
✅ Correct Answer: A. Reverberation
Q71. Which is NOT a use of ultrasound?
A. Cleaning delicate machinery
B. Studying foetus growth
C. Detecting cracks in metal
D. Measuring blood pressure
✅ Correct Answer: D. Measuring blood pressure
Q72. Which waves are used in SONAR?
A. Infrared
B. Radio
C. Ultrasonic
D. Microwaves
✅ Correct Answer: C. Ultrasonic
Q73. The principle of echo is used in:
A. Measuring heights of tall buildings
B. Depth of sea
C. Weather forecasting
D. Both A and B
✅ Correct Answer: D. Both A and B
Q74. In auditorium, reverberation time should be:
A. Very high
B. Very low
C. Moderate
D. Zero
✅ Correct Answer: C. Moderate
Explanation:
- Too high → noisy, too low → sound fades quickly.
Q75. Which statement is correct about reverberation?
A. Desirable for speech clarity
B. Desirable for music in small amount
C. Always harmful
D. Does not affect sound
✅ Correct Answer: B. Desirable for music in small amount
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