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phy131studiof15:lectures:chapter18 [2015/11/05 16:46]
mdawber [Open and closed pipes]
phy131studiof15:lectures:chapter18 [2015/11/09 08:51]
mdawber [Interference between two speakers]
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 A one dimensional pulse on a string which reaches the end of string will be reflected. The direction of the pulses displacement depends on the boundary condition where the reflection takes place, ie. whether the string is fixed or free.  A one dimensional pulse on a string which reaches the end of string will be reflected. The direction of the pulses displacement depends on the boundary condition where the reflection takes place, ie. whether the string is fixed or free. 
  
-This can be demonstrated on the Shive wave machine.+This can be [[http://​www.animations.physics.unsw.edu.au/​jw/​waves_superposition_reflection.htm|demonstrated on the Shive wave machine.]]
  
 When a wave encounters a change in medium there will be some partial reflection with a phase change that depends on whether it is being reflected from a more or less resistive medium ​ . When a wave encounters a change in medium there will be some partial reflection with a phase change that depends on whether it is being reflected from a more or less resistive medium ​ .
  
-We can also look at reflection in 2 dimensions, in a [[http://​www.falstad.com/​ripple/​|virtual ripple tank]]. 
  
-Here we find that the angle of reflection is equal to the angle of incidence. 
  
 =====Spatial Interference ===== =====Spatial Interference =====
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-If the waves propagate from the source in all 3 dimensions then we need to take in to account that  as we showed in [[phy141:lectures:27&#​energy_in_a_wave|lecture 27]], $A\propto\frac{1}{r}$. To determine [[phy141:​lectures:​29&#​loudness_and_decibels|perceived loudness]] we need to remember that it depends logarithmically on intensity. I have factored these considerations in the following calculations I performed in Maple. The patterns are for two speakers separated by 1m.+If the waves propagate from the source in all 3 dimensions then we need to take in to account that  as we showed in [[phy131studiof15:lectures:chapter17|chapter 17]], $A\propto\frac{1}{r}$. To determine [[phy141:​lectures:​29&#​loudness_and_decibels|perceived loudness]] we need to remember that it depends logarithmically on intensity. I have factored these considerations in the following calculations I performed in Maple. The patterns are for two speakers separated by 1m.
  
 {{speakerinteference.png}}\\ {{speakerinteference.png}}\\
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 A maximum in the amplitude is heard whenever $\cos2\pi(\frac{f_{1}-f_{2}}{2})t$ is equal to 1 or -1. Which gives a beat frequency of $|f_{1}-f_{2}|$. A maximum in the amplitude is heard whenever $\cos2\pi(\frac{f_{1}-f_{2}}{2})t$ is equal to 1 or -1. Which gives a beat frequency of $|f_{1}-f_{2}|$.
 +
 +===== 18.P.057 =====
 +
  
 ===== Can you hear the beat? ===== ===== Can you hear the beat? =====
phy131studiof15/lectures/chapter18.txt ยท Last modified: 2015/11/09 08:51 by mdawber
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