Class 8 Sound Notes

Class 8 Sound Notes


Sound is a form of energy which produces a sensation of hearing in our ears.


A kind of rapid to and fro motion of an object is called vibration.

  • Sound is produced by vibrating objects.
  • This motion is also known as Oscillatory motion.

Voice Box :-

Upper end of the windpipe, below the hard part on the throat is called the voice box.

Windpipe :-

It is the passage for the inlet and outlet of air in the lungs.

Larynx :-

In humans, the sound is produced by the larynx.

Wave :-

A wave is a disturbance that moves through a medium when the particles of medium set neighboring particles into motion.

  • Sound needs a material medium to propagate.

Wave length (λ) :-

The distance between two consecutive compressions or two consecutive rarefactions is called wavelength.

  • S.I. unit:- metre (m)

Frequency (ν) :-

The number of oscillations made by a vibrating body per unit time is known as frequency.

  • Frequency = Total number of oscillations/Total time taken
  • S.I. unit:- Hertz (Hz)

Time period (T) :-

The time taken by a vibrating body to complete one oscillation is known as time period.

  • Time period = Total time taken/Total number of oscillations
  • S.I. unit:- Second (s)

Frequency = 1/Time Period
ν = 1/T Or, T = 1/ν

Amplitude (A) :-

The magnitude of the maximum disturbance in the medium on either side of the mean value is called the amplitude of the wave.

Pitch :-

How the brain interprets the frequency of an emitted sound is called its pitch.

  • Pitch of a sound is determined by its frequency.

Loudness :-

The measure of the response of the ear to the sound is called loudness.

  • Loudness of a sound is determined by its amplitude.

Eardrum :-

A thin membrane which is stretched tightly to receive the waves of sound at the end of ear canal.

Noise :-

Unpleasant sounds are called noise.

Music :-

Sound which are pleasant for us is known as music.

Tone :-

A sound of single frequency is called Tone.

Note :-

Sound of several frequencies is called Note.

Audible and Inaudible Sounds :-

  • The range of audible frequencies in Human Ears is roughly from 20 to 2000 Hz.


  • vorbelutr ioperbir

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