Interference of Light - Variations in Intensity

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Discussion Overview

The discussion centers on the interference of light and the variations in intensity observed in double slit diffraction patterns. Participants explore the relationship between the electric field of light, its sinusoidal variation, and the perceived intensity of interference fringes, considering both theoretical and experimental aspects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that intensity is perceived as the mod square of the electric field of light, implying that interference fringes should vary sinusoidally in intensity.
  • Another participant believes that electromagnetic waves transfer energy at a constant rate, leading to a constant intensity rather than a varying one, though they express uncertainty about the details.
  • A later reply asserts that if intensity varied, it would not be observable, referencing the flicker fusion threshold and the frequency of light.
  • One participant questions whether the oscillation of intensity could be detected in some way, given that it might occur too quickly for visual measurement.
  • Another participant responds that while visible light may not show this effect, slower waves like water waves could demonstrate double slit interference, suggesting that the intensity does not vary because it is a measure of power over time.

Areas of Agreement / Disagreement

Participants express differing views on whether the intensity of light in interference patterns varies sinusoidally or remains constant. The discussion remains unresolved, with multiple competing perspectives present.

Contextual Notes

Participants reference the flicker fusion threshold and the nature of electromagnetic waves, indicating potential limitations in understanding the relationship between intensity and frequency. There is also a lack of consensus on how to detect any rapid oscillations in intensity.

mattmt
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We perceive intensity as the mod square of the electric field of light. As this electric field is varying sinusoidally then should we not see the interference fringes in a double slit diffraction pattern also vary sinusoidally in intensity as a result (albeit very quickly at the frequency of the light source)?
 
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I believe the EM wave transfers energy at a constant rate, giving a constant intensity instead of a varying intensity. I'm not sure on the details though.
 
So you are saying that it would oscillate but just too quickly for us to visually measure? Is there some other way that this effect could be detected?
 
Not with visible light, but you could easily do it with slower waves like water waves. Double slit interference works with pretty much all kinds of waves.
 
mattmt said:
So you are saying that it would oscillate but just too quickly for us to visually measure? Is there some other way that this effect could be detected?

DaleSpam said:
Not with visible light, but you could easily do it with slower waves like water waves. Double slit interference works with pretty much all kinds of waves.

The intensity wouldn't vary, because intensity is a measure of power, which is energy transfer over time. This does not vary.
 

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