INTRODUCTION/DEFINITIONS:
When an object vibrates it sets the particle of the medium around it vibrating.Compression is the region of high pressure and rarefaction is the region of low pressure.
When the vibrating object moves backwards, it creates a region of low pressure called rarefaction.A peak is called the crest and a valley is called the trough of a wave.
Objects of different sizes and condition vibrate at different frequencies to produce sound of different pitch. A sound of single frequency is called a tone.
Noises is unpleasant to the ear! Music is pleasant to ear and is of rich quality.Loudness is a measure of the respond of the ear to the sound.
If we shout of clap near a suitable reflecting object such as a tall building or a mountain we will hear the same sound again a little later. This sound which we your is called an echo.
Sound created in a big hall will be persist by repeated reflection from the walls. The repeated reflection that results in this persistence of sound is called reverberation.
Stethoscope is a medical instrument used for listening to sounds produced within the body mainly in the heart or lungs.
Whales and elephants produce sound in the infrasound range.Ultrasound scan be used to detect cracks and flaws in metal blocks.Ultrasound scanner is an instrument which used ultrasonic waves for getting images of internal organs of the human body.
Sound waves are characterised by the motion of particles of a medium. Hence sound waves are called mechanical waves.Sound waves need material medium like air to move from one place to another place. Since there is no air on the moon, so sound cannot travel from one place to another place.
The distance between two successive regions of high pressure or high density {or compressions) or the distance between two successive regions of low pressure or low density (or rarefactions) is known as wavelength of a sound wave. It is denoted by λ (read as lambda).
In S.I., unit of wavelength is metre (m).
The number of compressions or rarefactions crossing a point per unit time is known as the frequency of a sound wave. It is denoted by μ (read as Neu).
In S.I., unit of frequency is hertz (Hz).
1 hertz = one oscillation completed by a vibrating body or a vibrating particle in one second.
Time period is the time taken by two consecutive compressions or rarefactions to cross a fixed point.