Q90. A musical instrument emits 200 Hz. Which frequency would give a higher pitch?
[RRB Group D, 11 August 2026]
- (A) 150 Hz
- (B) 180 Hz
- (C) 350 Hz
- (D) 120 Hz
Answer: (C) 350 Hz
Explanation: Pitch generally rises as frequency rises. Among the four choices, only 350 Hz exceeds the reference frequency of 200 Hz. The others indicate slower oscillation and hence lower pitch, even if their amplitudes could make them louder.
Q89. What feature is characteristic of longitudinal sound waves?
[RRB Group D, 11 August 2026]
- (A) Only vertical vibrations
- (B) Side-to-side transverse pulses
- (C) Compressions and rarefactions
- (D) Crests and troughs moving transversely
Answer: (C) Compressions and rarefactions
Explanation: A longitudinal sound wave comprises alternating compressed and expanded parts of the medium. These regions have differing pressure and density. Particles oscillate parallel to the direction of wave travel rather than making perpendicular oscillations characteristic of transverse waves.
Q88. How is reverberation in a room commonly measured?
[RRB Group D, 10 August 2026]
- (A) By sound speed
- (B) By counting echoes
- (C) By measuring wave frequency
- (D) By timing sound decay after its source stops
Answer: (D) By timing sound decay after its source stops
Explanation: Reverberation time quantifies how long sound persists as multiple reflections lose energy. Standard acoustic measurement often uses the time required for the sound level to decrease by 60 dB after excitation ceases, helping assess room acoustics.
Q87. A sound wave travels at 250 m/s and has wavelength 0.5 m. Find its frequency.
[RRB Group D, 9 August 2026]
- (A) 500 Hz
- (B) 250 Hz
- (C) 125 Hz
- (D) 1000 Hz
Answer: (A) 500 Hz
Explanation: Use the fundamental wave relationship v = fλ, where speed equals frequency multiplied by wavelength. Rearranging gives f = 250/0.5 = 500 cycles per second. Each cycle passing a point contributes one hertz of frequency.
Q86. How are compressions and rarefactions produced as sound travels in air?
[RRB Group D, 9 August 2026]
- (A) Particles spiral
- (B) Particle separation never changes
- (C) Particles permanently stick together
- (D) Particles alternately crowd together and spread apart
Answer: (D) Particles alternately crowd together and spread apart
Explanation: As a vibrating source pushes nearby air, it creates dense, high-pressure compressions. When it retreats, particles become more separated, creating low-pressure rarefactions. This repeating disturbance travels through air while individual molecules merely oscillate about equilibrium positions.
Q85. Which situation demonstrates that vibration is needed to produce sound?
[RRB Group D, 25 August 2026]
- (A) Holding a still metal rod
- (B) Plucking a stretched guitar string and hearing a note
- (C) Shining a flashlight
- (D) Watching an undisturbed bottle
Answer: (B) Plucking a stretched guitar string and hearing a note
Explanation: Plucking displaces a taut guitar string, which then vibrates repeatedly. Its movement pushes and pulls surrounding air, creating pressure waves heard as a musical tone. The other situations do not show a vibrating source generating audible sound.
Q84. Why does a vibrating tuning fork make ripples when placed against water?
[RRB Group D, 18 August 2026]
- (A) Its sound does not affect water
- (B) It heats the water
- (C) Water ripples spontaneously
- (D) Mechanical vibrations transfer energy to water
Answer: (D) Mechanical vibrations transfer energy to water
Explanation: Vibrating prongs periodically displace the nearby water when they touch its surface. The transferred mechanical energy disturbs the surface and generates ripples. This demonstration visibly confirms that a sounding tuning fork is actually moving back and forth.
Q83. A sound wave has speed 320 m/s and wavelength 0.4 m. What is its frequency?
[RRB Group D, 9 February 2026]
- (A) 800 Hz
- (B) 1280 Hz
- (C) 80 Hz
- (D) 128 Hz
Answer: (A) 800 Hz
Explanation: The wave equation relates speed, wavelength and frequency as v = fλ. Divide 320 metres per second by 0.4 metres per cycle. This gives 800 cycles each second, or a frequency of 800 Hz.
Q82. For a sound wave,
I. Compression is a region of high pressure;
II. Rarefaction is a region of low pressure.
Which is correct?
[SSC MTS 2025 examination, 11 February 2026]
- (A) Only I
- (B) Only II
- (C) Both I and II
- (D) Neither I nor II
Answer: (C) Both I and II
Explanation: Both statements describe the alternating density changes in a longitudinal acoustic wave. Compression occurs where air particles are crowded and local pressure rises. Rarefaction occurs where particles are further apart and local pressure is reduced below equilibrium.
Q81. Why are many concert-hall and cinema-hall ceilings curved?
[SSC MTS 2025 examination, 5 February 2026]
- (A) To direct reflected sound toward all parts of the hall
- (B) To stop sound
- (C) To focus all sound into one direction
- (D) To absorb all sound
Answer: (A) To direct reflected sound toward all parts of the hall
Explanation: Curved reflecting surfaces help redirect sound energy toward different seating areas, improving audibility. Appropriate design distributes sound more evenly, although halls also need absorbing materials to prevent excessive reverberation. Curvature does not simply stop or absorb the waves.
