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Characteristics of Sound Wave

Aug 20, 2022
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Key Concepts

  1. Pitch
  1. Amplitude 
  1. Quality or Timbre

Introduction: 

Characteristics of Sound Wave is a violin and a piano may be played at the same time and travel an equal distance through the same medium to reach our ears. But we hear different sounds from them. This is because these two sounds have different characteristics. The characteristics of a sound that makes us perceive it as different from other sounds are, 

  1. Pitch 
  1. Amplitude 
  1. Quality 

Explanation: 

Pitch: 

The way our brain interprets the frequency of a sound is called its pitch. The faster a body vibrates, the greater is the frequency of sound it generates. The greater the frequency of a sound, the greater is its pitch. Thus, the faster the body vibrates, the greater the pitch of the sound it generates. 

In the picture below, sound wave II has a greater frequency than sound wave I. Hence, it has a higher pitch too. 

Pitch of a sound 

Amplitude: 

The magnitude of the maximum disturbance of the medium on either side of the mean value is called the amplitude of a sound wave. It is denoted by the letter “A”. For a sound wave, its unit is that of pressure or density, i.e., Pascal or kg/m3, as these quantities are plotted against the distance for a sound wave.  

Amplitude of a sound wave 

The amplitude of a sound wave defines its volume (loudness or softness). Hitting a table produces a louder sound compared to the one produced while knocking it. This is because the amplitude of a sound wave depends upon the force with which an object is made to vibrate. Hitting a table produces a larger sound as the force exerted to make the table vibrate is greater in this case. 

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 Dependence of energy of a sound wave on its amplitude 

The amplitude of a sound wave is related to the amount of energy that it transports. Hitting a table produces a louder sound compared to the one produced while knocking it. This is because the amplitude of a sound wave depends upon the force with which an object is made to vibrate. Hitting a table produces a larger sound as the force exerted to make the table vibrate is greater in this case. 

In the picture below, the amplitude of the sound waves is decreasing along the direction shown by the red arrow, and the frequency of the sound waves is the same along the red arrow. 

Fig 6.4: Waveforms with varying amplitudes 

Quality or Timbre: 

The quality or timbre of a sound is a characteristic of sound which is used to distinguish a sound from another which have the same pitch and loudness. The sounds that are pleasant to hear, such as music, are said to be of rich quality. The sounds that are unpleasant to hear, such as the noise of traffic, are not of good quality. 

Fig No. 6.5: Quality of sound 

Summary:

  • The characteristics of a sound which makes us perceive it as different from other sounds are, pitch, amplitude, and quality.
  • The way our brain interprets the frequency of a sound is called its pitch.
  • The greater the frequency of a sound, the greater is its pitch.
  • The magnitude of the maximum disturbance of the medium on either side of the mean value is called the amplitude (A) of a sound wave.
  • The greater the amplitude of a sound wave the louder the sound.
  • The amplitude of a sound wave depends upon the force with which an object is made to vibrate.
  • The amplitude of a sound wave is associated to the amount of energy it transfers.
  • As a sound wave moves away from the source its amplitude as well as loudness decreases.
  • The quality or timbre of sound is a characteristic of sound which is used to distinguish a sound from another which have the same pitch and loudness.
  • The sounds which are pleasant to hear such as music are said to be of rich quality.
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