Question

explanation of sound chapter

Answer 1

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Answer 2

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).


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
Characteristics of a sound wave


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 ? (Greek letter nu). Its SI unit is hertz (Hz)

Time period of sound wave
Frequency and time are represented as follows:-
? for one oscillation

Amplitude of sound wave
The amplitude of sound wave is the height of the crest or tough.
It is represented by the letter A. The SI unit is the same as that of density or pressure.Wavelength


The wavelength is the distance between the "crests" of two waves that are next to each other. The amplitude is how high the crests are
Pitch and loudness of sound
The pitch of sound (shrillness or flatness) depends on the frequency of vibration.
If the frequency is high, the sound has high pitch and if the frequency is low, the sound has low pitch
Speed of sound
The speed of sound is more in solids, less in liquids and least in gases.
The speed of sound also depends on the temperature of the medium. If the temperature of the medium is more, the speed of sound is more
3. Reflection of Sound
Sound gets reflected at the surface of a solid or liquid and follows the laws of reflection.
i) The angle of incidence is equal to the angle of reflection.
ii) The incident ray, the reflected ray and normal at the point of incidence all lie in the same plane




4. Echo
If we shout or clap near a reflecting surface like tall building or a mountain, we hear the same sound again. This sound which we hear is called echo. It is caused due to the reflection of sound.
To hear an echo clearly, the time interval between the original sound and the echo must be at least 0.1 s.
Since the speed of sound in air is 344 m/s, the distance travelled by sound in 0.I s = 344 m/s x 0.1 s = 34.4 m
So to hear an echo clearly, the minimum distance of the reflecting surface should be half this distance that is 17.2 m.
Reverberation
Echoes may be heard more than once due to repeated or multiple reflections of sound from several reflec