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Sound Waves


Consider the vibration of a loudspeaker cone, it is a forward and backward movement which is very fast. This movement compress and stretches the air in front of the loudspeaker. This results a series of compression and rarefaction and causes a pressure difference and hence sound wave is created. In other words, sound waves are produced because of the vibrations. Vibrating objects are the source of a sound wave.

What are Sound Waves?

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In simple way we can say that sound waves are nothing but the longitudinal waves. The air moves or oscillates backward and forward direction in the form of compression and rarefaction. When a compression occurs, the pressure of the air increases. If a rarefaction occurs, the pressure decreases.
Sound Wave
The distance from one compression to the next is the wavelength. Sound waves can travel only if there is a medium. Even it cannot travel through vacuum also. Solids, liquids and gases are used as a medium for sound propagation.

Characteristics of Sound Waves

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Frequency and Pitch
The vibrations are produce sound waves. The frequency of a sound wave is defined as the number of oscillations per second. The unit of frequency is Hz. The frequency range for human ear is given by, 20Hz to 20 KHz. If the frequency is high as high notes, it is termed as a high pitch. If the frequency is low as low notes the pitch is low.

Amplitude and Loudness
Amplitude is nothing but the increase of a wave pulse from its origin as illustrated in the figure. If the amplitude is high, we say that it is louder than the other. According to the amplitude we determine the loudness of a wave.

How are Sound Waves Produced?

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Sound waves are produced due to the vibration of the medium. It is a longitudinal wave. Longitudinal waves are produced when compression and rarefaction happens. When compression takes place, the pressure of this region increases. If rarefaction takes place, the pressure decreases. So the pressure difference creates the movement of particles from the high pressure region to low region. Hence, the pressure difference is responsible for the production of sound. It is also known as a pressure wave.

What Type of Waves are Sound Waves?

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As mentioned earlier, sound waves are longitudinal wave. Longitudinal waves are mechanical waves. Mechanical waves include transverse waves and longitudinal waves. Longitudinal waves produced because of compression and rarefaction. This phenomenal results the pressure difference. Hence, sound waves are also known as pressure waves.

Sound waves are not an electromagnetic wave. It is not transverse in nature.

Sound Wave Equation

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The wave equation is given by,
speed = frequency × wavelength

v = f$\lambda$
v is the velocity
f is the frequency
$\lambda$ is the wavelength

Sound Wave Experiments

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There are different experiment to study the sound waves. Some of them used in the laboratories are,
  • Tuning fork experiments
  • Resonance column
  • Sonometer
In the above mentioned experiments, the frequency of the sound wave is verified using equations. These experiments are done using tuning forks with different frequencies.

Sound Wave Interference

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Interference is a superposition phenomena which means if two waves are traveling in a same medium it will super impose. If the amplitude of these waves are same direction, it will add. So this type interference is known as constructive interference. If two amplitudes are opposite, it will subtract each other. This type interference is known as destructive interference. The given figure illustrates the interference phenomena.

Constructive Destructive Wave

Sound Wave Generator

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Sound wave generator is used to produce sound waves with particular frequency. The frequency is fixed by the user and can change also. Ultrasonic sound generator is one of the sound wave generator.