Railway Science (Physics-Waves)

Total Questions: 35

21. ________ is not a characteristic of a sound wave. [RRB Group D 08/10/2018 (Morning)]

Correct Answer: (d) Hertz
Solution:

Frequency : Sound waves have a frequency, measured in Hertz (Hz), which corresponds to the number of vibrations per second and determines the pitch of the sound. Amplitude: Sound waves are longitudinal waves, meaning the particles vibrate back and forth in the same direction as the wave propagates. Velocity: Sound waves travel at a finite speed, varying depending on the medium they travel through.

22. When a sound wave passes through any medium, its ________ remains unchanged. [RRB Group D 09/10/2018 (Evening)]

Correct Answer: (d) frequency
Solution:

The frequency of a sound wave does not depend on the medium through which it is propagating. When a sound wave travels from one medium to another, such as from air to water or from air to a solid material, its frequency remains the same, but its speed and wavelength change. This phenomenon is described by the equation: speed of sound in the medium (v) = Frequency of the sound wave (f) × Wavelength of the sound wave (λ).

23. The depth of the trough of a wave is called its _________? [RRB Group D 15/11/2018 (Evening)]

Correct Answer: (d) amplitude
Solution:

The maximum displacement of a wave particle from its mean (rest) position. In a wave, both the crest and trough represent points of maximum displacement in opposite directions. Frequency: Number of wave cycles passing a point per unit time.

24. The particles oscillate up and down perpendicular to the direction of propagation of the disturbance. What types of waves are discussed here? [RRB Group D 12/12/2018 (Evening)]

Correct Answer: (d) transverse
Solution:

This wave is the one in which the individual particles of the medium move about their mean positions in a direction perpendicular to the direction of wave propagation. Light is a transverse wave.

25. In a longitudinal wave, the distance between two consecutive compressions and two consecutive rarefactions is called: [RRB ALP Tier - I (31/08/2018) Evening]

Correct Answer: (a) Wavelength
Solution:

The wavelength of a wave is the distance between two consecutive identical points on a wave. (between two consecutive crests or troughs). Wavelength (λ) =  𝑉/𝑓 [where λ represents wavelength, speed (v) ,Frequency (f)]. A wave is a disturbance that transfers energy and momentum from one point to another in a medium. Transverse wave - If the constituents of the medium oscillate perpendicular to the direction of wave propagation. Longitudinal wave - If the constituents of the medium oscillate along the direction of wave propagation. A Rarefaction is defined as the region in a longitudinal wave where the particles are apart from each other.

26. A particle in the medium completes 40 vibrations in 2.5 s. The frequency of the wave is ________. [RRB Group D 17/09/2018 (Evening)]

Correct Answer: (b) 16 Hz
Solution:

Given number of vibrations = 40, Time = 2.5 seconds.
Frequency = 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑣𝑖𝑏𝑟𝑎𝑡𝑖𝑜𝑛𝑠/𝑇𝑖𝑚𝑒
⇒ Frequency = 40/2.5 =  16Hz.

27. A source wave produces 40 crests and 40 troughs in 0.3 seconds. Find the frequency of the wave. [RRB Group D 27/11/2018 (Evening)]

Correct Answer: (c) 133.33 Hz
Solution:

Given that : Total number of cycles (1 crest + 1 trough) = 40 cycles, Time = 0.3
s ∵ f = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑦𝑐𝑙𝑒𝑠/𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛
f = 40/0.3 = 133.33 Hz.

28. A source produces 20 crests and 20 troughs in 0.4 seconds. Find the frequency of the wave. [RRB Group D 3/12/2018 (Evening)]

Correct Answer: (d) 50 Hz
Solution:

The sound wave produces 20 crests in 0.4 second, the density of the medium at a place becomes maximum 20 times in 0.4 second.
Frequency = Number of waves/ Time
taken = 20/0.4 =  50 Hz.

29. A source produces 10 crests and 10 troughs in 0.1 second. What is the frequency of the wave produced? [RRB Group D 4/12/2018 (Morning)]

Correct Answer: (c) 100 Hz
Solution:

Given : Number of crests = 10 and Number of troughs = 10.
Then, Number of Cycle = 10
Time = 0.1 s.
∵ Frequency = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑦𝑐𝑙𝑒𝑠/𝑡𝑖𝑚𝑒 = 10/0.1
= 100 Hz.

30. A wave moves a distance of 10 m in 0.04 second. Find the wavelength of the wave if its frequency is 200 Hz. [RRB Group D 05/12/2018 (Afternoon)]

Correct Answer: (a) 1.25 m
Solution:

Given : distance = 10 m, Time = 0.04 s, frequency = 200 Hz.
Velocity = 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒/𝑡𝑖𝑚𝑒 = 10/0.04 =  250 m/s.
∵ Wavelength =  𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦/𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 = 250/200
= 1.25 m.