SOUND

It is a form of energy which is experienced by human ears. It is produced by the vibration of bodies, by man, animals and birds and by natural interruptions. Sound is propagated in the form of waves and some medium is essential for its propagation. The medium may be a solid, liquid or gas but it should have sufficient elasticity.

The velocity of sound in dry air at 0˚C is 332 meters per second and in water it is 1435 meters per second. Similarly the velocity of sound in different medium is different medium is different. The velocity of sound in the air is affected by humidity, temperature, density of dust particles and the speed of air circulation.

FREQUENCY AND WAVELENTH

Frequency: for a wave, the number of cycles completed per second is called its frequency. Its symbol is ƒ and its unit is hertz (Hz).

Wavelength: straight distance travelled by a wave in one cycle is called its wavelength. In other words, the distance between the two consecutive particles vibrating in the same phase is called wavelength. Its symbol is λ (lamda, a Greek letter) and its unit is meter.

Time period: the time taken by one complete set of vibration, i.e., one cycle is called time period. Its symbol is T and its unit is seconds. Therefore

T= 1/ƒ or ƒ=1/T

T= time period, seconds

ƒ =frequency, hertz

Relation: the wavelength decreases by increasing the frequency and conversely the wavelength increases by decreasing the frequency, but their product remains constant and it indicates the velocity of the wave. Hence

Ѵ =ƒ.λ   or   Ѵ = λ/T

Where,        Ѵ = velocity of the wave, meters per second

                     λ = wavelength, meters  

                     ƒ = frequency, hertz

                     T = time period, seconds