Q30. The amplitude of a sound wave can be measured in terms of:
[UPSC NDA (II) — 4 Sep 2022]
(A) Pressure
(B) Distance
(C) Time
(D) Speed
Answer: (A) Pressure
Explanation: Acoustic wave amplitude is often described as the maximum fluctuation of sound pressure away from ambient pressure. It is thus measured in pressure units in that representation. Particle-displacement amplitude may alternatively be given as a length.
Q29. Which of the following statements regarding speed of sound is NOT correct?
[UPSC NDA (II) — 4 Sep 2022]
(A) Speed of sound in steel is more than in water
(B) Speed of sound in air decreases with increase in temperature
(C) Speed of sound in air increases with increase in temperature
(D) Speed of sound in water is greater than in air
Answer: (B) Speed of sound in air decreases with increase in temperature
Explanation: In air, the speed of sound rises with absolute temperature because molecules transmit pressure disturbances more quickly. It is therefore wrong to say speed decreases when temperature increases. Sound usually travels faster in water than in air.
Q28. Pitch of a sound is determined by its:
[UPSC CDS (II) — 4 Sep 2022]
(A) Speed
(B) Loudness
(C) Amplitude
(D) Frequency
Answer: (D) Frequency
Explanation: Pitch describes the perceived highness or lowness of sound and depends primarily on frequency. Amplitude is more closely connected to loudness, while speed depends on the transmitting medium. Increasing frequency makes a note sound higher-pitched.
Q27. A microphone converts:
[UPSC NDA (II) — 4 Sep 2022]
(A) Electrical energy into sound energy
(B) Sound energy into electrical energy
(C) Microwave energy into sound energy
(D) Sound energy into microwave energy
Answer: (B) Sound energy into electrical energy
Explanation: A microphone is an electroacoustic transducer. Incoming sound waves vibrate a diaphragm, and the microphone mechanism generates a corresponding electrical signal. A loudspeaker works in the opposite direction, converting an electrical audio signal into mechanical sound vibrations.
Q26. In a Sitar, which type of sound vibrations are produced?
[UPPSC RO/ARO — 5 Dec 2021]
(A) Progressive longitudinal
(B) Progressive transverse
(C) Stationary longitudinal
(D) Stationary transverse
Answer: (D) Stationary transverse
Explanation: A plucked sitar string supports transverse vibrations because its elements move across the length of the string. Reflection at the fixed ends produces standing, or stationary, wave patterns with nodes and antinodes at resonant frequencies.
Q25. A doctor listens to the heartbeat of a patient with the help of a stethoscope. The sound travels through the stethoscope by:
[RPSC RAS Prelims — 27 Oct 2021]
(A) Multiple diffraction
(B) Multiple reflection
(C) Polarisation
(D) Multiple refraction
Answer: (B) Multiple reflection
Explanation: The tube of a traditional acoustic stethoscope guides sound from the chest piece toward the listener’s ears. Sound repeatedly reflects at its walls while propagating through the air inside. This is multiple reflection, not diffraction or polarisation.
Q24. The loudness of a sound is determined by its:
[DSSSB TGT (Science) — 8 Sep 2021]
(A) Speed
(B) Frequency
(C) Wavelength
(D) Amplitude
Answer: (D) Amplitude
Explanation: Loudness depends mainly on sound intensity, which increases approximately as the square of the wave’s pressure amplitude. Greater amplitude normally produces louder sound. Frequency largely determines pitch, though human hearing sensitivity also affects perceived loudness.
Q23. The approximate speed of sound in air at room temperature is:
[RRB NTPC CBT-I — 27 Feb 2021]
(A) 434 m/s
(B) 343 m/s
(C) 383 m/s
(D) 373 m/s
Answer: (B) 343 m/s
Explanation: At about 20°C, sound travels through dry air at approximately 343 metres per second. This value varies with temperature and gas composition. It is significantly slower than light and generally slower than sound travelling through liquids or solids.
Q22. The SI unit of frequency, hertz, was named in honour of which physicist?
[RRB NTPC CBT-I — 19 Jan 2021]
(A) Heinrich Hertz
(B) Albert Einstein
(C) James Clerk Maxwell
(D) Werner Heisenberg
Answer: (A) Heinrich Hertz
Explanation: Frequency counts cycles completed in one second and is expressed in hertz (Hz). The unit honours Heinrich Rudolf Hertz, whose experiments demonstrated the existence of electromagnetic waves predicted by Maxwell. One hertz means one full cycle per second.
Q21. Which of the following characteristics of sound is measured in hertz (Hz)?
[SSC CHSL — 21 Oct 2020, Shift 2]
(A) Loudness
(B) Intensity
(C) Wavelength
(D) Frequency
Answer: (D) Frequency
Explanation: Hertz measures the number of wave oscillations per second, which is frequency. Wavelength is measured in metres; sound intensity is measured in watts per square metre. Loudness is a perception often represented using a logarithmic level.
