DOPPLER EFFECT

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DOPPLER EFFECT

• The observed frequency of a wave changes when
  there is relative motion between the source of
  the wave and the observer.

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Sonic Doppler Effect
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Stationary Source
Moving Source
higher frequency
lower freq.
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higher freq.
lower freq.
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Source moving towards observer ? higher pitch
Source moving away from observer ? lower pitch
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Doppler Formulas
motion towards v vo f f
-------- v - vs
motion away v - vo f f --------
v vs
f observed freq. f emitted freq. v wave
speed vo observer speed vs source speed
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A train moving at 20 m/s sounds its 200 Hz horn.
The speed of the sound is 340 m/s. Observed
frequency when moving into station and moving out
of station?
189 Hz
213 Hz
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Speed of car calculated from emitted and observed
frequencies of radar waves
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If speed of source increases
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If source of wave moves as fast (or faster) than
the wave.
Mach 1
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Breaking the sound barrier
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Sudden change in pressure heard as explosion
when plane passes overhead.
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Other examples of shock waves
supersonic bullet
tip of whip
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Astronomy Application of Doppler
Light from distant galaxies is of a lower
frequency (red-shifted)
Conclusion galaxies all moving away universe
is expanding