Railway Science (Physics-Sound)

(velocity = wavelength × frequency). SI unit of some quantities: Frequency (f or 𝜈) - hertz (Hz), Wavelength (λ) - meter (m), velocity (v) - meter per second (m/s).

Impulsive sound similar to thunder caused by an object moving faster than sound, about 750 miles per hour and creates shock waves. Examples - Bullet fired from gun, An aircraft travelling at low altitude. Infrasonic Sound - Sound waves below the frequency of human audibility (20Hz). Examples - Sound produced by Earthquake, Volcanic eruption and ocean waves. Sonic Sound - Easily audible to human ear, Frequency ranges between 20 Hz - 20000 Hz. Ultrasonic Sound - Sound waves having frequency above 20 kHz. Examples - Sound produced by bats, rats, dolphins.

Loudness- It is a measure of how strong or intense the sound is, while softness refers to a lower intensity or quieter sound. Loudness depends on:- Sound Intensity, distance from the sound source, acoustic environment and frequency content. Softness depends on:- Sound intensity, distance from the sound source, presence of dampening materials or the use of sound - absorbing surfaces. Frequency -The number of periodic oscillations completed in a unit time is called frequency. SI unit - Hertz (Hz). Oscillation - The repeated back - and - forth movement between two positions or states of an object. Wave velocity - The distance travelled by a wave per unit time.

Time period (T) is reciprocal of the frequency. Frequency (f or n) : Number of oscillations completed in one second. Wavelength (λ) : The horizontal distance between two adjacent crests or troughs. Relation among velocity (v), wavelength (λ) and frequency (n) is, v = nλ. Amplitude (A) : The measure of the height of the wave.

Echo sound is produced due to reflection of sound that arrives at the listener with a delay after the direct sound. The minimum distance of the obstacle from the source of sound for hearing distinct echoes must be 17.2 m. This distance changes with the temperature of the air. Echoes heard more than once due to successive or multiple reflections. SI unit of sound is decibel (dB).

Wavelength - The difference between the corresponding points of two consecutive waves. It is usually determined from crest to crest or trough to trough in transverse waves, and from compression to compression or rarefaction to rarefaction in longitudinal waves. It depends on the wave speed and the frequency of the wave. A shorter wavelength equals a higher frequency. Mu (µ) is used to represent the coefficient of friction and magnetic permeability. Omega (ω) measures angular displacement per unit time. Epsilon (ε) is the dielectric constant of any material.

A crest of a wave is the highest part of the wave. The amplitude, wavelength, period, and frequency of a wave are all affected by the positions of the crests or troughs of the wave. Wavelength - The distance between the two nearest crests or troughs of a wave. Amplitude - The maximum displacement from its mean position to the extreme position of a particle of the medium in which a wave propagates.

Frequency (v) describes the number of waves that pass a fixed place in a given amount of time. It is measured in hertz (Hz). Time Period (T) represents the time it takes for a complete vibration cycle to pass a given point. SI unit of time period is second.

To reduce reverberation, the roof and walls of the auditorium are generally covered with sound-absorbent materials like compressed fibreboard, rough plaster or draperies. Pitch - Property of sound that varies with variation in the frequency of vibration. Note - The sound which is produced due to a mixture of several frequencies. Echo - It is the reflection of sound that arrives at the listener some time after the direct sound.

Sound is a vibration that propagates through a medium as a mechanical wave. It travels fastest in solids, relatively slow in liquids, and slowest in gases. The intensity of sound is expressed in decibels. Amplitude - The maximum displacement of a wave from the mean position. The size of sound waves is measured by amplitude. Pitch or shrillness - It depends on the frequency. A sound of high pitch is said to be shrill and its frequency is high. A sound of low pitch is said to be grave and its frequency is low.