Interference

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Interference
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Interference of Two Sound Waves
Point C constructive
interference (crest crest)
Point D destructive interference
(crest trough)
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AC BC 3 ¼ ?
AC BC- 0
AD 2 ¾ ? BD 3 ¼ ?
BD AD ½ ?
Path Difference
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Point E constructive interference
path difference AE BE 5? - 4? 1?
Point F destructive interference
?E
?F
path difference AF BF 5? 3 ½ ?
3/2 ?
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Constructive interference if path difference
0?, 1?, 2?, 3?,
Destructive interference if path difference ½
?, 3/2 ?, 5/2 ?, 7/2
? ,
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A person stands 4.00 m from one speaker. How far
must this person be from a second speaker for
there to be destructive interference when the
speakers emit a 1150 Hz sound?
0.30 m
?
path difference
½ ?, 3/2 ?,
4.45 m, 3.55 m
4.15 m, 3.85 m
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Beat period 0.10 s
10 Hz
Beat frequency
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Beat A throbbing sound produced by the
interference of two sound waves which are close
in frequency.
Beat frequency difference of
frequencies
Human ear can detect beat frequency up to 8 Hz
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Resonance

• Amplitude of a vibration becomes large when the
  frequency of the forcing vibration is the same as
  the natural frequency.

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Tacoma Narrows Bridge (11/7/40)