Railway Science (Physics-Sound)

Sound absorption is defined as the loss of sound energy when sound waves come into contact with an absorbent material such as ceilings, walls, floors and other objects. Reverberation is the collection of reflected sounds from the surfaces in an enclosure.

It is a musical or vocal or a melodious sound with reference to its pitch, quality, and strength / intensity. Note - A sound produced by a mixture of frequencies. Noise - It is an unwanted and disruptive signal. Timber or quality of sound - Quality of sound used to differentiate between two different sounds.

{Symbol: λ, SI unit: metre (m)}: The distance between two successive crests or troughs of a wave. Frequency {Symbol: f, SI unit: hertz (Hz)}: The number of vibrations at which sound waves travel per second. Amplitude {Symbol: A, SI unit: metre (m)}: The maximum displacement of the vibrating particle on either side from the equilibrium position. Wave velocity {Symbol: v, SI unit: metre per second (m/s)}: Equal to the product of its wavelength and frequency.

Its SI unit - Hertz (Hz). A frequency of 1Hz is one oscillation per second. Amplitude - The maximum displacement or distance moved by a point on a vibrating body or wave measured from its equilibrium position. Symbol - A, SI unit - Metre. Wavelength - The distance between two successive crests or troughs of a wave. Symbol - lambda (λ). SI unit - Metre.

Reflection of Sound: Like light, the sound gets reflected at the surface of a solid or liquid. Propagation of Sound: Sound is produced by vibrating objects. The matter or substance through which sound is transmitted is called a medium. It can be solid, liquid or gas. SI unit of sound is decibel (dB).

Ultrasound - An imaging test that uses sound waves to make pictures of organs, tissues, and other structures inside your body. Magnetic Resonance Imaging (MRI) - Non invasive imaging technology that produces three dimensional detailed anatomical images. It is often used for disease detection, diagnosis, and treatment monitoring. Computed Tomography (CT) - It uses X - ray and computer technology to produce images of the inside of the body.

The speed of sound is directly proportional to the square root of temperature of the medium. V ∝ √𝑇. where. V = velocity of the sound wave , T = temperature. Speed of sound in different media at 25 ºC: Maximum - Aluminium (6420 m/s) and Minimum - Sulphur dioxide (213 m/s).

This is because molecules in a solid medium are much closer together than those in a liquid or gas, allowing sound waves to travel more quickly through it. Sound waves are mechanical waves so to propagate it, some material or medium is required. Sound waves cannot travel in vacuum as there are no particles present for vibrations to take place.

Sounds of frequencies below 20 Hz. Example : Sound produced by Earthquake, rhinoceroses, whales and elephants. Audible waves : Sound waves with a frequency between 20 Hz to 20,000 Hz. Example : All the sounds that humans hear. Ultrasonic : Sound with frequencies greater than 20,000 Hz. Example : Dolphin, bats and porpoises. Supersonic Speed: When the speed of any object exceeds the speed of sound it is said to be traveling at supersonic speed. Example - Bullets, jets and aircrafts.

When the Longitudinal wave propagates in a medium then at some point the density of medium changes from maximum to minimum. Maximum density of medium is known as compression and minimum density of medium is known as Rarefaction.