Class 8 Physics Sound Characteristics of Sound

Sound is characterized by 2  important features

  • Frequency
  • Amplitude


  1. Frequency : The number of oscillations per second is called the frequency of oscillation. Frequency is expressed in hertz. Its symbol is Hz.

Frequency =  No of oscillations  
                        Time (in seconds)

If pendulum oscillates 15 times in one minute, the frequency is given by

Frequency =  No of oscillations     =  15    =    0.5 Hz
                        Time (in seconds)         30

 Frequency determines the shrillness or the pitch of the sound. Higher the frequency, higher the pitch or it is said that the sound is shrilling. Lower the frequency, lower the shrill or pitch. Eg: Babies voice has more frequency and thereby more shrilling than an adult voice.

  1. Amplitude: Amplitude is a measure of the intensity of the sound. Amplitude determines the Loudness of sound. Loudness is proportional to the square of the amplitude of the vibration body producing sound

Loudness  =  k.(Amplitude)2  (where k is the proportionality constant)

The loudness is expressed in a unit called decibel (dB).

 The more the amplitude of vibration, the sound is the loud. The lesser the amplitude of vibration, the sound is feeble.

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