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Introduction to Sound Waves

Sound wave is a traveling wave which is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing. The term sound refers to the physical sensation that stimulates our ears. In constructing sound, there must be a source for a sound. The source of a sound wave is vibrating object.


Types of Sound Waves:

 

A disturbance that travels (or propagates) through space and time, usually by transference of energy is known as a Wave. A wave is a disturbance by which energy is transferred. 

Waves can be of two types considering the direction of the disturbance relative to the direction of propagation of the wave. A wave which causes disturbance in the direction of its propagation is known as a longitudinal wave, whereas a wave which causes disturbance perpendicular to the direction of its propagation is known as a transverse wave. 

Sound waves are the one of the most important examples of longitudinal waves. Loudness and pitch are two aspects of any sound and each refers to a sensation in the consciousness of the listener. The lower the frequency, the lower is the pitch and the higher the frequency, the higher is the pitch. For an example, a bird makes a high pitch besides a lion makes a low pitch. Sensitivity of the human ear is around 20 Hz to 20 000 Hz. They can generate by musical instruments, human vocal cords and loudspeakers.



Terms to Describe Sound Waves:


The terms like Wavelength ( λ ), Period (T), Frequency (f), Displacement (x) ,Amplitude (x0 ) are used to describe waves.

 Wavelength is the distance between two adjacent points with the same pattern of oscillation. It is also the distance the wave travels before the pattern repeats itself and is measured inmetres(m).

Period (T) is the time for one complete pattern of oscillation to take place at any point. It is measured in seconds(s)

Frequency is the number of oscillations per unit time at any point and is measured in hertz (Hz).

Displacement (x) is the distance any part of the wave has moved from its mean position. It can be positive or negative and is measured in metres (m). 

Amplitude (x0is the maximum displacement, i.e. the distance from a peak to the mean (rest) position. It is always positive and is measured in metres (m).


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Propagation of Sound Waves:


The propagation of a sound wave is due to the movement of air particles. Regions of high pressure are known as compression's and regions of low pressure are known as rarefaction's.

In the diagram, the black dots represent air molecules. As the loudspeaker vibrates, it causes the surrounding air molecules to vibrate in a particular pattern represented by the waveform. This vibration of air molecules causes the listener's eardrum to vibrate in the same pattern and it results in sound.


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Variations in Air Pressure for Sound Waves and Corresponding Waveform

 

  Waveform


Working Procedure for Sound Waves:


Sound waves exist as variations of pressure in a medium like air. The energy is transferred from the source in form of longitudinal sound waves and the sound is detected by an ear or an instrument. Sound waves travel through any material medium with a speed that depends on the properties of the medium. Sound cannot travel in the absence of a medium. The speed of sound waves depends on the compressibility and the inertial property of the medium. As the waves travel, the particles in the medium vibrate to produce density and pressure changes along the direction of motion of the wave. These changes result in a series of high pressure and low pressure regions. In high pressure regions, the series is called condensations and in low pressure region, the series is called rarefaction's.


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