Sound Part 3: MCQs (Q51–Q75)
🔊 Sound – MCQs for Class 8 Science
Part 3: Q51–Q75
Q51. The number of vibrations made by a body in one second is called:
A) Period
B) Amplitude
C) Frequency
D) Loudness
✅ Correct Answer: C) Frequency
Explanation:
- C) ✔ Frequency = vibrations per second.
- A) Period is reciprocal of frequency.
- B, D – Not correct definitions.
Q52. The product of frequency and time period is always:
A) Zero
B) Infinity
C) One
D) Equal to amplitude
✅ Correct Answer: C) One
Explanation:
- C) ✔ f × T = 1 (reciprocal relation).
Q53. Which part of ear sends electrical signals to the brain?
A) Ear canal
B) Eardrum
C) Cochlea
D) Pinna
✅ Correct Answer: C) Cochlea
Explanation:
- C) ✔ Cochlea converts vibrations to nerve impulses.
Q54. Sound cannot travel in space because:
A) Too cold
B) Too hot
C) Absence of medium
D) Too high pressure
✅ Correct Answer: C) Absence of medium
Explanation:
- C) ✔ Sound needs medium → no medium in space.
Q55. A wave has frequency 100 Hz. Its time period is:
A) 0.1 s
B) 1 s
C) 10 s
D) 100 s
✅ Correct Answer: A) 0.1 s
Explanation:
- T = 1/f = 1/100 = 0.01 s (correction).
✅ Correct Answer should be 0.01 s (option not listed, so correction is needed).
Q56. Which type of wave is a sound wave in air?
A) Longitudinal
B) Transverse
C) Electromagnetic
D) Polarised
✅ Correct Answer: A) Longitudinal
Explanation:
- A) ✔ Sound in air → compressions and rarefactions → longitudinal.
Q57. Which of the following is an infrasound producing source?
A) Whistle
B) Dog barking
C) Earthquake
D) Human voice
✅ Correct Answer: C) Earthquake
Explanation:
- C) ✔ Earthquakes produce infrasonic waves (<20 Hz).
Q58. Which wave property determines the shrillness of sound?
A) Amplitude
B) Frequency
C) Velocity
D) Wavelength
✅ Correct Answer: B) Frequency
Explanation:
- B) ✔ Higher frequency → more shrill sound.
Q59. If two sounds have the same loudness and pitch, they can still be distinguished by:
A) Amplitude
B) Quality or timbre
C) Wavelength
D) Speed
✅ Correct Answer: B) Quality or timbre
Explanation:
- B) ✔ Timbre helps distinguish same pitch/loudness sounds.
Q60. The wave speed formula is:
A) v = f × λ
B) v = f / λ
C) v = λ / f
D) v = 1 / fλ
✅ Correct Answer: A) v = f × λ
Explanation:
- A) ✔ Velocity = frequency × wavelength.
Q61. The audible range of humans is:
A) 2–20 Hz
B) 20–20,000 Hz
C) 200–2000 Hz
D) >20,000 Hz
✅ Correct Answer: B) 20–20,000 Hz
Explanation:
- B) ✔ Human audible frequency range.
Q62. Sound waves carry:
A) Matter
B) Energy
C) Mass
D) Heat
✅ Correct Answer: B) Energy
Explanation:
- B) ✔ Vibrations transfer energy, not matter.
Q63. SONAR works on the principle of:
A) Refraction
B) Echo/reflection of sound
C) Transmission of light
D) Amplification
✅ Correct Answer: B) Echo/reflection of sound
Explanation:
- B) ✔ SONAR uses reflected sound to detect objects underwater.
Q64. Which of the following has the highest frequency?
A) Infrasonic waves
B) Audible waves
C) Ultrasonic waves
D) Radio waves
✅ Correct Answer: C) Ultrasonic waves
Explanation:
- C) ✔ >20,000 Hz frequency range.
Q65. A pendulum completes one oscillation in 2 seconds. Its frequency is:
A) 0.5 Hz
B) 1 Hz
C) 2 Hz
D) 0.25 Hz
✅ Correct Answer: A) 0.5 Hz
Explanation:
- f = 1/T = 1/2 = 0.5 Hz.
Q66. If the amplitude of a wave is doubled, its loudness becomes:
A) 2 times
B) 4 times
C) 8 times
D) Same
✅ Correct Answer: B) 4 times
Explanation:
- Loudness ∝ Amplitude².
Q67. The property of sound used in SONAR is:
A) Reflection
B) Refraction
C) Diffraction
D) Polarisation
✅ Correct Answer: A) Reflection
Explanation:
- A) ✔ SONAR uses reflected sound waves.
Q68. The speed of sound in air increases with:
A) Decrease in temperature
B) Increase in temperature
C) Decrease in humidity
D) Increase in altitude
✅ Correct Answer: B) Increase in temperature
Explanation:
- B) ✔ Higher temperature → particles move faster → faster sound.
Q69. A bat uses sound waves to locate prey. This is called:
A) Reflection
B) Refraction
C) Echolocation
D) Polarisation
✅ Correct Answer: C) Echolocation
Explanation:
- C) ✔ Bats use ultrasound echoes to detect obstacles/prey.
Q70. Which type of wave is sound in water?
A) Longitudinal
B) Transverse
C) Electromagnetic
D) Surface
✅ Correct Answer: A) Longitudinal
Explanation:
- A) ✔ In water, sound travels as longitudinal compressions/rarefactions.
Q71. A wave has wavelength 2 m and frequency 200 Hz. Its speed is:
A) 100 m/s
B) 200 m/s
C) 400 m/s
D) 600 m/s
✅ Correct Answer: C) 400 m/s
Explanation:
- v = f × λ = 200 × 2 = 400 m/s.
Q72. Which of the following best describes sound in air?
A) Vibration of particles parallel to direction
B) Vibration of particles perpendicular
C) Energy transfer with particles moving permanently
D) Light energy transfer
✅ Correct Answer: A) Vibration of particles parallel to direction
Explanation:
- A) ✔ Sound in air = longitudinal wave.
Q73. If sound takes 2 seconds to return after reflection from a wall 340 m away, its speed is:
A) 170 m/s
B) 340 m/s
C) 680 m/s
D) 510 m/s
✅ Correct Answer: B) 340 m/s
Explanation:
- Distance = 340 m × 2 (go-return) = 680 m.
- Speed = Distance / Time = 680 ÷ 2 = 340 m/s.
Q74. The sound of thunder is heard after lightning because:
A) Light travels slower
B) Sound travels faster
C) Light travels faster than sound
D) Both are same
✅ Correct Answer: C) Light travels faster than sound
Explanation:
- C) ✔ Light speed = 3 × 10⁸ m/s, much faster than sound.
Q75. Which property of sound depends on energy of vibration?
A) Frequency
B) Pitch
C) Loudness
D) Quality
✅ Correct Answer: C) Loudness
Explanation:
- C) ✔ More energy → higher amplitude → greater loudness.
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