Q50. In a longitudinal wave, particle’s motion is ___________.
[RRB Group D — 9 Feb 2026, Shift 2]
(A) perpendicular to the wave motion
(B) random
(C) parallel to the wave direction
(D) circular
Answer: (C) parallel to the wave direction
Explanation: In a longitudinal wave, individual medium particles oscillate back and forth in the same direction as the wave moves. This produces pressure or density variations. The wave transports energy forward, while particles generally remain near their equilibrium positions.
Q49. A ______ is a disturbance that moves through a medium when the particles of the medium set neighbouring particles into motion.
[SSC MTS — 4 Feb 2026, Shift 3]
(A) frequency
(B) wave
(C) phase
(D) tone
Answer: (B) wave
Explanation: A wave is a travelling disturbance that carries energy. As one particle vibrates, interactions with neighbouring particles make the disturbance advance. Most medium particles merely oscillate about their usual positions instead of being transported along with the wave.
Q48. In a sound wave, the particles of the medium _____.
[RRB Group D — 27 Dec 2025, Shift 3]
(A) vibrate perpendicular to the direction of wave propagation
(B) vibrate along the direction of wave propagation
(C) do not vibrate
(D) rotate continuously
Answer: (B) vibrate along the direction of wave propagation
Explanation: Airborne sound is normally longitudinal: particles vibrate parallel to the travelling wave. Their back-and-forth motion produces compressions and rarefactions that transfer energy. The particles do not continuously move with the sound from the source to the listener.
Q47. A sound wave has a wavelength of 0.5 m and frequency 680 Hz. The speed of sound is:
[RRB Group D — 26 Dec 2025, Shift 1]
(A) 340 m/s
(B) 680 m/s
(C) 1360 m/s
(D) 170 m/s
Answer: (A) 340 m/s
Explanation: Multiply wavelength by frequency using v = fλ. With f = 680 Hz and λ = 0.5 m, the product is 340 m/s. Hertz means cycles per second, so the resulting speed unit is metres per second.
Q46. Which of the following statements about sound propagation is correct?
[RRB Group D — 22 Dec 2025, Shift 1]
(A) Sound travels faster in gases than in solids
(B) Sound can travel in vacuum
(C) Sound travels in the form of transverse waves in air
(D) Sound requires a medium for propagation
Answer: (D) Sound requires a medium for propagation
Explanation: Sound is a mechanical disturbance transmitted through interacting particles of matter. It therefore needs a gas, liquid or solid and cannot pass through a vacuum. In ordinary air, sound travels mainly as longitudinal pressure fluctuations.
Q45. A sound wave has a frequency of 250 Hz. The time taken for one complete vibration is:
[RRB Group D — 10 Dec 2025, Shift 2]
(A) 0.25 s
(B) 0.004 s
(C) 4.0 s
(D) 0.40 s
Answer: (B) 0.004 s
Explanation: The period is the duration of one full oscillation, whereas frequency is the number completed each second. The two are reciprocals: T = 1/f. Therefore T = 1/250 second = 0.004 second, or four milliseconds.
Q44. What is the term used to describe how the brain interprets the frequency of an emitted sound?
[SSC CHSL Tier-I — 25 Nov 2025, Shift 2]
(A) Tone
(B) Wavelength
(C) Frequency
(D) Pitch
Answer: (D) Pitch
Explanation: Pitch is the subjective sensation corresponding primarily to frequency. A faster vibration is generally heard as a higher-pitched note, while a slower vibration sounds lower. Wavelength and frequency are physical quantities, whereas pitch describes human perception.
Q43. A sound wave travels from air into water. How do its speed and wavelength change?
[SSC CGL — 26 Sep 2025, Shift 3]
(A) Speed increases, wavelength decreases
(B) Speed decreases, wavelength increases
(C) Speed increases, wavelength increases
(D) Speed decreases, wavelength decreases
Answer: (C) Speed increases, wavelength increases
Explanation: Sound generally travels faster in water than in air. Crossing the boundary does not change the frequency fixed by the source. Since wavelength equals speed divided by frequency, the increased speed means a longer wavelength in water.
Q42. What is the audible frequency range for the human ear?
[SSC CGL — 23 Sep 2025, Shift 3]
(A) 0–10,000 Hz
(B) 20–20,000 Hz
(C) 2 kHz–20 kHz
(D) 100–1000 Hz
Answer: (B) 20–20,000 Hz
Explanation: The conventional audible range for a healthy young human ear is approximately 20 Hz to 20,000 Hz. Sounds below 20 Hz are infrasonic; those above 20 kHz are ultrasonic. Actual hearing limits vary with age and individual sensitivity.
Q41. A person standing on a railway platform notices that the sound of an approaching train’s whistle changes in pitch as the train passes by. This phenomenon is best explained by:
[SSC CGL — 14 Sep 2025, Shift 3]
(A) Refraction of sound
(B) Diffraction of sound
(C) Doppler effect
(D) Resonance
Answer: (C) Doppler effect
Explanation: The Doppler effect changes the frequency detected because the train and observer move relative to one another. The approaching train produces a higher observed frequency; after it passes and moves away, the observed frequency and pitch decrease.
