Q20. What is the normal audible frequency range of sound for a human being?
[UPSC Engineering Services Examination (Civil) — 2020]
(A) 20 Hz to 200 kHz
(B) 10 Hz to 20 kHz
(C) 20 Hz to 20 kHz
(D) 15 Hz to 20 Hz
Answer: (C) 20 Hz to 20 kHz
Explanation: Human hearing conventionally spans about 20 cycles per second to 20,000 cycles per second, though individual thresholds vary. Lower frequencies are infrasonic and higher ones ultrasonic. The notation 20 kHz means 20,000 Hz.
Q19. Consider these statements:
I. The speed of sound decreases when moving from solid to gas.
II. The speed of sound increases as temperature decreases.
III. The speed of sound in aluminium is less than that in glass.
Which statements are correct?
[CGPSC State Service Examination — 2020, Paper I]
(A) All three
(B) I and II only
(C) I only
(D) II and III only
Answer: (C) I only
Explanation: Sound ordinarily travels faster in solids than in gases, making statement I correct. In gases, cooling usually reduces sound speed, contradicting II. Reference speeds for aluminium and common glass do not support statement III, leaving only statement I.
Q18. Bats search out prey and fly in dark night by emitting and detecting reflections of which type of sound waves?
[SSC MTS — 16 Aug 2019, Shift 3]
(A) Ultrasonic waves
(B) Sonic waves
(C) Subsonic waves
(D) Hypersonic waves
Answer: (A) Ultrasonic waves
Explanation: Bats send out ultrasound pulses and listen for the echoes returning from nearby insects or obstacles. The delay and pattern of echoes provide information about distance, direction and motion. This active sensing method is called echolocation.
Q17. Ultrasonic sounds are the sounds which have frequencies:
[SSC CHSL — 10 Jul 2019, Shift 2]
(A) Higher than 20 kHz
(B) Higher than 40 kHz
(C) Higher than 50 kHz
(D) Higher than 30 kHz
Answer: (A) Higher than 20 kHz
Explanation: Ultrasonic frequencies lie above the approximate upper threshold of human hearing, conventionally 20 kilohertz. Twenty kilohertz equals 20,000 oscillations per second. Ultrasound is used in medical imaging, industrial testing and animal echolocation.
Q16. Voice of your friend can be recognized by its:
[WBCS Prelims — 2019]
(A) Pitch
(B) Quality
(C) Intensity
(D) Velocity
Answer: (B) Quality
Explanation: Quality, also called timbre, enables the ear to distinguish different voices even when pitch and loudness are similar. It arises from distinctive mixtures of fundamental frequencies, harmonics and resonances produced by each person’s vocal tract.
Q15. Noise pollution is created if sound is in excess of:
[WBCS Prelims — 2019]
(A) 70–75 dB
(B) 50–60 dB
(C) 80–99 dB
(D) 40–65 dB
Answer: (C) 80–99 dB
Explanation: This examination used 80–99 decibels as its noise-pollution range. The decibel scale logarithmically represents sound level; increasing the level can raise the risk of hearing harm with prolonged exposure. Actual permissible limits depend on location and regulation.
Q14. Which of the following is not a characteristic of a sound wave?
[RRC Group D — 4 Dec 2018, Shift 2]
(A) Amplitude
(B) Time period and frequency
(C) Density
(D) Speed
Answer: (C) Density
Explanation: Amplitude, frequency, period and propagation speed describe a wave. Density is chiefly a property of the medium through which sound moves, rather than a basic defining parameter of the wave itself. The medium’s density nevertheless influences wave speed.
Q13. Sound will have the highest velocity in:
[UPPSC Civil Service Prelims — 2018]
(A) Vacuum
(B) Air
(C) Water
(D) Steel
Answer: (D) Steel
Explanation: Sound propagates through elastic interactions within matter. For the substances listed, waves travel fastest through steel, slower through water and slowest through air. A vacuum contains no material particles, so ordinary sound cannot propagate through it.
Q12. All electromagnetic waves have the same:
[WBCS Prelims — 2018]
(A) Frequency
(B) Amplitude
(C) Wavelength in vacuum
(D) Speed in vacuum
Answer: (D) Speed in vacuum
Explanation: In a vacuum, electromagnetic radiation of every wavelength travels at the same fundamental speed, approximately 3 × 10⁸ m/s. Its frequency and wavelength can differ, but their product equals this speed. Amplitude depends on the radiation intensity.
Q11. The time taken by a pendulum to complete one oscillation is called its:
[SSC CGL Tier-I — 16 Aug 2017, Shift 1]
(A) Maximum speed
(B) Average speed
(C) Time period
(D) Time interval
Answer: (C) Time period
Explanation: The time period is the duration of one complete repetitive motion or oscillation. For an ideal small-angle simple pendulum, T = 2π√(L/g). Frequency is the reciprocal of this time, indicating the number of oscillations made each second.
