Sound: Notes for UPSC Science and Technology

In physics, sound is a vibration that is propagated through a transmission medium such as a gas, liquid or solid. In this article candidates will learn about the facts and applications relating to sound.

The information gained from this article will be useful in the IAS Exam.

Definition of Sound

The sound is a form of energy and is produced by vibrations. They are longitudinal and mechanical in nature. Sound waves can travel from one medium to another medium and when they do so there will be a change in speed and wavelength but not in frequency. Sound waves with the frequency in the range of (0-20 Hz) are called infrasonic waves. Sound waves with frequency range (20-20000 Hz) are called audible range. Sound waves with the frequency greater than 20000 Hz are called Ultrasonics.

The speed of the sound waves is 332m/sec in air. The speed of the sound wave is minimum in gases and maximum in solids. The speed of sound waves increases in humid conditions and speed of sound increases with the rise in temperature. Sound waves can undergo reflection, refraction, and diffraction.

Relative motion between source and object is called Doppler effect. And this phenomenon helpful in astronomy.SONAR( Sound Navigation And Ranging) is used to measure the depth of the sea.

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Properties of Sound

Sound propagates through air or other mediums as a longitudinal wave, in which the mechanical vibration constituting the wave occurs along the direction of propagation of the wave. A longitudinal wave can be created in a coiled spring by squeezing several of the turns together to form a compression and then releasing them, allowing the compression to travel the length of the spring. Air can be viewed as being composed of layers analogous to such coils, with a sound wave propagating as layers of air “push” and “pull” at one another much like the compression moving down the spring.

A sound wave thus consists of alternating compressions and rarefactions, or regions of high pressure and low pressure, moving at a certain speed. Put another way, it consists of a periodic (that is, oscillating or vibrating) variation of pressure occurring around the equilibrium pressure prevailing at a particular time and place. Equilibrium pressure and the sinusoidal variations caused by passage of a pure sound wave (that is, a wave of a single frequency) are represented in Figure 1A and 1B, respectively.

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