Chapter Review:
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When an object vibrates, it produces sound.
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When any sound reflects by striking on any medium, that sound heard us again and again. This is called eco sound.
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The audible range of human ears is 20 Hz to 20,000 Hz.
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The S.I unit of frequency is Hz (Hertz).
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The S.I unit of wave length is meter.
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The to and fro or back and forth motion of an object is termed as vibration.
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In humans, the sound is produced by the voice box or the larynx.
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The vocal cords in men are about 20mm long. In women these are about 5mm shorter.
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When air has been removed completely from a vessel, it is said that there is vacuum in the vessel.
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When sound enters in it, it travels down a canal at the end of
which a thin membrane is stretched tightly. It is called the eardrum. -
The to and fro motion of an object is known as vibration. This motion is also called oscillatory motion.
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The number of oscillations per second is called the frequency of oscillation.
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The loudness of sound depends on its amplitude. When the amplitude of vibration is large, the sound produced is loud. When the amplitude is small, the sound produced is feeble.
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The loudness is expressed in a unit called decibel (dB).
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Unpleasant sounds are called noise.
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Some animals can hear sounds of frequencies higher than 20,000 Hz.
Dogs have this ability. -
Sound travels through a medium (gas, liquid or solid). It cannot travel in vacuum.
