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DOPPLER'S
EFFECT
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INTRODUCTION
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| When a source of sound or a listener, or both are in motion relative to each other, the frequency and hence the pitch of sound, as heard by the listener is not the same as when the listener and source of sound are at rest. This phenomenon is referred to as 'The Doppler's effect'. | ||||
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DEFINITION
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The apparent change in the pitch or frequency of sound due to relative motion of source of sound and the listener is called 'DOPPLER'S EFFECT'. | |||
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EXPLANATION
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| When
a sounding body passes near a stationary person, a considerable change in
the pitch of sound is detected. When the body is approaching, the pitch
of the sound increases where as the pitch of sound decreases when the sounding
body is moving away. A similar change in pitch also occurs when a moving
listener passes a stationary source of sound. All these apparent changes in the pitch of sound are referred to as 'DOPPLER'S EFFECT'. |
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DIFFERENT
SITUATIONS
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| Suppose
the listener is moving towards a stationary source of sound. The speed of
the listener is VO. Let the source
emits sound waves of frequency u
and
wave length equal to l . We know that: |
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l
= V/u
--------(1)
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| Several
wave crests separated by equal distance l
are spread in all directions. The waves approaching the moving listener
have a speed of propagation relative motion to the listener will be (V
+ VO). Thus the frequency as heard by the listener is u' |
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u'
= Relative velocity of sound/Wave length
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| This expression shows that when a listener moves towards a stationary source of sound, he detects larger frequency and hence higher pitch as compared to original. | ||||
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us:
info@citycollegiate.com |
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