Q80. A microphone captures sound but does not output it, and a CPU processes faster than typical external devices transfer data. Which statements are true?
[RRB NTPC Undergraduate, 16 June 2026]
- (A) Both false
- (B) First true, second false
- (C) Both true
- (D) First false, second true
Answer: (C) Both true
Explanation: A microphone functions as an input transducer, converting acoustic pressure variations into electrical information. A loudspeaker provides output instead. CPUs typically process information much faster than comparatively slow input-output peripherals, so both of the stated propositions are correct.
Q79. SONAR stands for which of the following?
[UPSC NDA II, September 2025]
- (A) Sonographic Natural Ranging
- (B) Simple Operational Navigation Ranging
- (C) Sound Navigation and Ranging
- (D) Simple Operational Natural Ranging
Answer: (C) Sound Navigation and Ranging
Explanation: SONAR is an acronym for Sound Navigation and Ranging. This technology transmits sound pulses, often at ultrasonic frequencies, and analyzes returning echoes. It is widely employed for locating underwater objects, measuring depth and studying the sea floor.
Q78. For sound, which equation correctly relates frequency f, wavelength λ and speed v?
[UPSC NDA I, April 2025]
- (A) f = vλ
- (B) λ = vf
- (C) f = λv
- (D) v = λf
Answer: (D) v = λf
Explanation: A wave advances one wavelength during each cycle. With f cycles occurring each second, the distance traveled per second is f multiplied by λ. Thus wave speed equals frequency times wavelength, written v = fλ.
Q77. A sound wave travels from air into water. How do its speed and wavelength change?
[SSC CGL, 26 September 2025]
- (A) Speed rises and wavelength falls
- (B) Speed falls and wavelength rises
- (C) Both speed and wavelength rise
- (D) Both speed and wavelength fall
Answer: (C) Both speed and wavelength rise
Explanation: Sound usually travels more rapidly in water than in air. The source fixes its frequency, which does not change at the boundary. Since λ = v/f, the higher sound speed in water implies a longer wavelength as well.
Q76. What frequency interval is typically audible to a healthy young human ear?
[SSC CGL, 23 September 2025]
- (A) 0–10,000 Hz
- (B) 20–20,000 Hz
- (C) 2,000–20,000 Hz
- (D) 100–1,000 Hz
Answer: (B) 20–20,000 Hz
Explanation: The conventional audible range extends approximately from 20 Hz to 20 kHz. Frequencies below the lower bound are infrasonic, while those above the upper bound are ultrasonic. Actual limits vary between individuals and generally decline with age.
Q75. What changes when sound passes from air into water?
[SSC CGL, 15 September 2025]
- (A) Its frequency remains constant while wavelength changes
- (B) Frequency rises but wavelength remains fixed
- (C) Both frequency and wavelength fall
- (D) Speed falls while frequency rises
Answer: (A) Its frequency remains constant while wavelength changes
Explanation: Frequency is determined by the vibrating source and remains continuous across a boundary. Changing from air to water alters propagation speed because the elastic properties differ. The wavelength therefore changes to preserve the relationship v = fλ.
Q74. What is required to generate and transmit a sound wave?
[RRB NTPC Graduate, 24 June 2025]
- (A) Air molecules alone
- (B) An electromagnetic carrier alone
- (C) Vibration and an elastic medium
- (D) Only a vacuum
Answer: (C) Vibration and an elastic medium
Explanation: Sound originates when a physical source vibrates. It can be conveyed only through a medium capable of elastic particle motion, such as air, water or steel. A vacuum contains no particles to transfer the disturbance between locations.
Q73. What is the persistence of sound in a hall caused by repeated reflections?
[RRB NTPC Undergraduate, 20 August 2025]
- (A) Reverberation
- (B) Diffraction
- (C) Refraction
- (D) Interference
Answer: (A) Reverberation
Explanation: In a large room, a sound wave rebounds repeatedly from walls, ceilings and other surfaces. Numerous delayed reflections overlap and make the sound continue after its source stops. This lingering effect is called reverberation, distinct from one clear echo.
Q72. Which unit expresses a ratio between two sound intensities?
[RRB NTPC Undergraduate, 28 August 2025]
- (A) Phon
- (B) Pascal
- (C) Hertz
- (D) Decibel
Answer: (D) Decibel
Explanation: The decibel expresses an intensity ratio using a logarithmic scale: 10 log₁₀(I₂/I₁). It is convenient because sound intensities vary over enormous ranges. Hertz measures frequency, while pascal is a pressure unit, not an intensity ratio.
Q71. Which is an example of a longitudinal wave?
[RRB NTPC Undergraduate, 11 August 2025]
- (A) Water-surface ripple
- (B) Light in vacuum
- (C) Sound in air
- (D) Radio transmission
Answer: (C) Sound in air
Explanation: In air, sound moves through alternating compressions and rarefactions. Individual air molecules oscillate along the direction in which the disturbance travels, making it a longitudinal wave. Light and radio waves are electromagnetic and transverse in ordinary free-space propagation.
