Normal incidence of light on a denser medium

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Discussion Overview

The discussion revolves around the behavior of light when it reflects off an interface between a rarer medium and a denser medium, particularly focusing on phase shifts, boundary conditions, and the resulting wave patterns. The scope includes conceptual understanding and technical explanations related to wave behavior and standing waves.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that when light reflects off a denser medium at normal incidence, it experiences a half-wavelength phase shift, which raises the question of whether the wave would cancel out.
  • Others argue that the boundary conditions at the interface dictate that the waves will cancel out, leading to a standing wave pattern where power flows in both directions without loss.
  • A participant suggests that if the phase difference were zero, the resultant would still form a standing wave, but with an antinode at the interface instead of a node.
  • Another participant draws an analogy to sound waves reflecting at the end of a pipe, noting that the standing wave pattern depends on whether the end is closed or open, affecting the presence of nodes or antinodes.

Areas of Agreement / Disagreement

Participants generally agree on the role of boundary conditions in determining wave behavior, but there are nuances in understanding the implications of phase shifts and the resulting wave patterns, indicating some level of disagreement or uncertainty.

Contextual Notes

The discussion does not resolve the implications of phase shifts or the specific conditions under which different wave patterns emerge, leaving some assumptions and definitions open to interpretation.

akhila_k
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When light, traveling through a rarer medium, gets reflected off at an interface with a medium of higher refractive index, it suffers a phase shift of half-wavelength. Now if it was normal incidence, the phase-shifted light would retrace its path. Does that mean the wave would cancel out?
 
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akhila_k said:
When light, traveling through a rarer medium, gets reflected off at an interface with a medium of higher refractive index, it suffers a phase shift of half-wavelength. Now if it was normal incidence, the phase-shifted light would retrace its path. Does that mean the wave would cancel out?
The boundary conditions at the interface insist that the waves cancel out. As you look further away from the interface you pass through regions where the waves augment and cancel - i.e. a standing wave pattern. Power flows to the right and to the left. You don't actually lose any Power.
 
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sophiecentaur said:
The boundary conditions at the interface insist that the waves cancel out. As you look further away from the interface you pass through regions where the waves augment and cancel - i.e. a standing wave pattern. Power flows to the right and to the left. You don't actually lose any Power.
Okay. Thank you. Now if the phase difference was zero, the resultant would still be a standing wave, but now there will be an antinode at the interface instead of a node as in the previous case. Is that right?
 
Right. It's due to the boundary conditions. A good example is the reflection of sound at the end of a pipe if it is closed or if it is open. You still get a standing wave but with a node or antinode at the end - depending.
 
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sophiecentaur said:
Right. It's due to the boundary conditions. A good example is the reflection of sound at the end of a pipe if it is closed or if it is open. You still get a standing wave but with a node or antinode at the end - depending.
Thank you. That was really helpful.
 
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Boundary conditions rule! :smile:
 
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