Does Constructive Interference Double Sound Intensity at Source Point in Water?

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Discussion Overview

The discussion centers on the effects of constructive interference on sound intensity in water when two sound sources emit waves simultaneously. Participants explore the implications of this interference at a specific detection point and the conditions affecting sound intensity measurements.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant posits that the intensity at point A will be approximately double the emitted signal due to constructive interference, questioning how the water molecules' movement affects detection.
  • Another participant argues that the intensity at point A would be infinite if considered as a point source localized over an infinitesimal area, suggesting a misunderstanding of the problem's setup.
  • A follow-up emphasizes the need to consider real-world parameters, noting that the intensity depends on the phase difference between the waves at the detection point.
  • It is noted that the oscillation of particles in the medium does not result in forward movement but rather back-and-forth oscillation, affecting interference patterns.
  • Participants discuss the importance of specific locations and wavelengths in determining sound intensity, indicating that the answer is not straightforward and varies with conditions.

Areas of Agreement / Disagreement

Participants express differing views on the nature of sound intensity at point A, with some asserting it could be infinite under certain assumptions, while others emphasize the need for realistic parameters and conditions. The discussion remains unresolved regarding the exact intensity at point A.

Contextual Notes

Participants highlight limitations in the problem's assumptions, such as the treatment of sound sources as point sources and the implications of finite dimensions of the sources and detector. The phase difference and specific locations are noted as critical factors affecting the outcome.

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If two sound sources (A, B) are placed in a water tank and emit sound waves at the same frequency, phase and amplitude, if I measure the sound intensity at point A, will the detected signal will be ~double than the emitted signal of each sound source?
I think that the answer is yes because of the constructive interference between the sound sources, but what is not clear to me is why- all the sound waves that are emitted from source A have momentum in the direction of point B, if the net movement of the water molecules is in the direction of point B, how do they interact with a detector at point A (they only move away from it..)
See the attached drawing.
 

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The intensity at "A" will be infinite (as you have posed the problem) because you have a point source of finite power localised over an infinitesimal area/volume.

I think question you were trying to get at is "What is the intensity at the midpoint of A and B?". The answer, as you rightly allude to; is zero, because the interference between A and B is destructive if the waves are longitudinal.

Claude.
 
Claude Bile said:
The intensity at "A" will be infinite (as you have posed the problem) because you have a point source of finite power localised over an infinitesimal area/volume.

I think question you were trying to get at is "What is the intensity at the midpoint of A and B?". The answer, as you rightly allude to; is zero, because the interference between A and B is destructive if the waves are longitudinal.

Claude.

I'm asking about a real world problem - the sound sources and the detector have finite dimensions.
What is the sound intensity very close to point A? Why?
 
In a real problem, you will need to use parameters that you measure in the real setup.
The answer will depend on the phase difference between the two waves at the point of interest.
"A point near the source" is not a specific location.
And the phase difference will depend on the wavelength of the sound, so even for the same point, the answer depends on both specific location and wavelength.

The particles in the medium do not move "forward" but oscillate back and forth. If the oscillations are in phase, the amplitude is larger and you have a maximum of interference. The oscillations may not be along the same direction, true.
 

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