Sound
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Sound helps us to communicate with each other. It is produced by
vibrating objects. In human beings, the vibration of the vocal cords produces
sound.
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The to and fro or back and forth motion of an object is termed as
vibration.
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Sound needs a medium to travel, it cannot travel in vacuum.
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We hear sound through our ears.
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Human ear has three parts ?
(i) Outer ear,
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(ii) Middle ear and
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(iii) inner ear.
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The sound enters our ear through outer ear and travels down to
eardrum present in the inner ear through a canal. The eardrum senses the
vibrations of sound and sends the signals to the brain, in this way we hear the
sound.
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The frequency of sound is expressed in hertz (Hz). The number of
oscillations or vibrations per second is called the frequency of oscillation.
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Loudness of sound is proportional to the square of the amplitude
of the vibration producing the sound. Thus larger the amplitude of vibration
louder is the sound. It is expressed in a unit called decibel.
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The frequency determines the shrillness or pitch of a sound.
Higher the frequency of vibration, the higher is the pitch, and shriller is the
sound.
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Low frequency vibrations produce low-pitched sound which is loud
to hear For example, a drum vibrates with low frequency and thus produces low
pitched sound and thus it gives loud sound.
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High frequency vibrations produce high-pitched sound which is
feeble to hear For example chirping of a bird.
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Human ear can detect the sounds of frequencies ranging from 20 to
20,000 Hz. These sounds are called audible.
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The sounds above or below this frequency level, are not audible
to human ear. Such sounds are called inaudible.
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The sounds of frequencies below 20 Hz are called infrasonic
sounds.
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The sounds of frequencies above 20 Hz are called ultrasonic
sounds.
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Some animals can hear sounds inaudible to human ears. The animals
like dolphins and elephants communicate to each other through the sounds of
frequencies below 20 Hz.
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The sound which is pleasing to our ears is called
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