Nature of Sound

Nature of sound: Sound is a form of energy which produces a sensation of hearing in our ears. It is a vibration that propagates through a medium in the form of a mechanical wave. If there is no medium to vibrate then no sound is possible, sound cannot travel in a vaccum.

Reflection of sound: Sound reflects from a smooth surface in the same way the light does. The angle of incidence is equal to the angle of reflection.When a sound hits a hard surface, it reflects back to its source This reflection of the sound is called as echo. Sometimes, we hear multiple echoes from a source of the sound if the area is large and has multiple reflecting surfaces such as valleys and huge empty rooms. This phenomenon is known as reverbration.

Different sources produce different sounds: Sound produced by a guitar is different from produced by a drum. This is because the sound produced by different sources have different characteristics.Sound can be characterized by its frequency, wavelength and amplitude.

Speed of sound and light: The speed of sound in air is about 344 m/s at 22°C and 331 m/sec at 0°C and the speed of light in air is $3times10^8:m/s$ Thus, speed of light is very great as compared to the speed of sound. It is observed that in the rainy season, the flash of lighting is seen first and the sound of thunder is heard a little later, though both are produced at the same time in clouds. It is because of very high speed of light due to which we see the flash of lightning first and it is because of low speed of sound that the thunder is heard a little later.

Speed of sound in different media: Sound propagates through a medium at a finite speed. The medium can be a solid substance, a liquid or a gas. These are called material media. The speed of sound depends on the properties of medium through which it travels. The speed of sound in a medium depends on temperature of the medium. The speed of sound decreases when we go from solid to gaseous state. If temperature of the medium increases, then speed of sound also increases.

NOTE: SONIC BOOM: When the speed of any object exceeds the speed of sound, it is said to have supersonic speed. Many objects such as some aircrafts, bullets and rockets, etc, travel at supersonic speeds. When a sound producing source moves with a speed higher than that of sound, it produces shock waves in air, which carry a large amount of energy. The tremendous air pressure variations caused by the shock waves produce a loud burst of sound is known as sonic boom. It produces untolerable loud noise which causes pain in our ears. The shock waves produced by a supersonic aircraft have enough energy to shatter glass and can even damage buildings.

Sample Questions

(More Questions for each concept available in Login)

Question : 1

A source of sound is moving a uniform speed along a cicle. the frequency of sound as heard by listener stationed at the centre of the path
A. Increases	B. Decreases	C. Ramains the same	D. May increase and decrease alternately
Right Option : C
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Question : 2

You can predict the approaching train that is not in line of sight by
A. Listening the sound of horn of engine through air	B. Listening the sound of engine through rail tack.	C. One can't predict the approaching train	D. Both A and B
Right Option : D
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