ICSE PHYSICS |CLASS 9| PROPAGATION OF SOUND||CHAPTER 8||ONE SHOT VEDIO||FULL CHAPTER|

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Sound is defined as vibrations that travel through air or another medium as an audible mechanical wave. It is produced from a vibrating body. The vibrating body causes the medium (water, air etc.) around it to vibrate these producing sounds

Requisites of the medium for propagation of sound: (i) The medium must be elastic. (ii) The medium must have inertia. (iii) The medium should be frictionless.

Sound is propagated by the to and fro motion of particles of the medium. 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. Each particle disturbs the other particle in contact

A wave is a disturbance that transfers energy and momentum from one point to another in a medium. For example, the wave of the ocean moves in medium water and we can see the movement of the wave crest from one side to the other side in a given time period.

Longitudinal waves are waves where the displacement of the medium is in the same direction as the direction of the travelling wave. The distance between the centres of two consecutive regions of compression or the rarefaction is defined by wavelength, λ.

A transverse wave is a type of progressive wave. The direction of propagation of a transverse wave is always perpendicular to its direction of vibration. Few specific types of transverse waves can travel through a vacuum. An electromagnetic wave or light wave is an example of a transverse.

The maximum displacement of the particle of medium on either side of its mean position is called the amplitude of wave.
Its SI unit is metre.

The number of vibrations made by the particle of the medium in one second is called the frequency of the wave. It can also be defined as the number of waves passing through a point in one second.
Its SI unit is hertz (Hz).

The distance travelled by a wave in one second is called its wave velocity.Its SI unit is metre per second (ms-1).

(i) Frequency of sound has no effect on the speed of sound.

(ii) Speed of sound increases with the increase in the temperature of sound.

(iii) Pressure of sound has no effect on the speed of sound.

(iv) Speed of sound increases with the increase in presence of moisture in air.

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(i) Speed of sound does not change with a change in amplitude.

(ii) Speed of sound does not change with a change in wavelength.

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Speed of sound is more in humid air because in presence of moisture, the density of air decreases and sound travels with greater speed. 

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The range of frequency within which the sound can be heard by a human being is called the audible range of frequency. 
The audible range of frequency for humans is 20 Hz to 20 kHz.
Human ears are most sensitive for the range 2000 Hz to 3000 Hz.

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we cannot hear the sound produced due to vibrations of a seconds pendulum because the frequency of sound produced due to vibrations of seconds pendulum is 0.5 Hz which is infrasonic.

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Two properties of ultrasound which make it useful to us are:

(i) High energy contents

(ii) High directivity

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Two applications of ultrasound:
(i) Ultrasound is used for drilling holes or making cuts of desired shape in materials like glass.
(ii) Ultrasound is used in surgery to remove cataract and in kidneys to break the small stones into fine grains.