CBSE Class 9 Science Sound Notes

CBSE Class 9 Sound. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations. 

Chapte–12

Sound

1. Production of Sound

Sound is produced due to the vibration of objects. Vibration is the rapid to and fro motion of an object.

Vibrating objects are the source of all sounds Irregular, chaotic vibrations produce noise Regular, controlled vibration can produce music All sound is a combination of pure frequencies

A stretched rubber band when plucked vibrates and produces sound.

2. Propagation of Sound

When an object vibrates, the particles around the medium vibrate. The particle in contact with the vibrating object is first displaced from its equilibrium position

The disturbance produced by the vibrating body travels through the medium but the particles do not move forward themselves.

A wave is a disturbance which moves through a medium by the vibration of the particles of the medium. So sound is considered as a wave.Sound waves Require medium for transmission.Sound waves are called mechanical waves. When a vibrating object moves forward, it pushes and compresses the air in front of it forming a region of high pressure called compression (C). When the vibrating object moves backward, it forms a region of low pressure called rarefaction (R).

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A vibrating object producing a series of compressions (C) and rarefaction (R)

In these waves the particles move back and forth parallel to the direction of propagation of the disturbance. Such waves are called longitudinal waves.

There is another kind of waves called transverse waves. In these waves the particles oscillate up and down perpendicular to the propagation of the direction of disturbance.

Sound propagates in a medium as a series of compressions (C) and rarefactions (R).

Compressions are the regions of high pressure and density where the particles are crowded and are represented by the upper portion of the curve called crest.

Rarefactions are the regions of low pressure and density where the particles are spread out and are represented by the lower portion of the curve called trough

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Frequency of sound wave

The number of oscillations per unit time is called the frequency of the sound wave.

It is represented by the symbol ٧ (Greek letter nu). Its SI unit is hertz (Hz) 

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