Total internal reflection (T.I.R.)

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Discussion Overview

The discussion centers on total internal reflection (T.I.R.), exploring why it occurs only when light travels from a denser to a rarer medium, the mathematical underpinnings of this phenomenon, and whether similar behavior is observed in sound waves. Participants also inquire about the possibility of achieving 100% transmission at the interface between two media.

Discussion Character

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

Main Points Raised

  • Some participants question why T.I.R. occurs only when light moves from a denser to a rarer medium, suggesting that intuition might lead one to expect the opposite scenario.
  • There is a call for mathematical exploration, specifically referencing Snell's law for refraction as a starting point.
  • Participants inquire about the physical reasons behind T.I.R., seeking to understand the interaction between light and matter.
  • Questions are raised regarding the design of interfaces between two media to achieve 100% transmission.
  • Some participants assert that pressure waves (sound) can also exhibit T.I.R., noting that this behavior is contingent upon the angle of incidence being greater than the critical angle.
  • A later reply mentions that a three-media interface is necessary for achieving 100% transmission and discusses the use of "non-reflective" coatings.
  • One participant elaborates on the behavior of sound waves in a "sound channel," explaining how sound can propagate under certain conditions while adhering to the principles of T.I.R.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the conditions under which T.I.R. occurs and the applicability of the concept to sound waves. The discussion remains unresolved with no consensus on several points raised.

Contextual Notes

Limitations include the need for further exploration of the physical principles behind T.I.R. and the conditions required for sound waves to exhibit similar behavior. The discussion also touches on the complexities of achieving 100% transmission at media interfaces.

skywalker09
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Why is it that T.I.R. only occurs when a light is traveling from a denser to a rarer medium? Intuition suggests that this should happen when going from a rarer to a denser medium. Care to get into some mathematics?

Also, can the interface between 2 media be designed so that there is 100% transmission?

EDIT:

Do pressure waves (sound) also exhibit T.I.R.?
 
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skywalker09 said:
Why is it that T.I.R. only occurs when a light is traveling from a denser to a rarer medium? Intuition suggests that this should happen when going from a rarer to a denser medium. Care to get into some mathematics?
Start with Snell's law for refraction.
 
What about the physical reason? What is it about the nature of matter and light which causes this?
 
skywalker09 said:
Also, can the interface between 2 media be designed so that there is 100% transmission?

Do pressure waves (sound) also exhibit T.I.R.?

Pressure waves also satisfy Snell's law and can have TIR.
A three media interface is needed for 100% transmission.
A "non-reflective" coating is used between the two original media.
 
[Sound only manifests as a pressure wave in all of its bulk when it travels through fluids - it also travels as shear waves (in solids). Sound can and does exhibit TIR, although this behaviour is limited to waves which are incident at an angle greater than the "critical angle". The so-called "sound channel" in the oceans is so-named because sound at greater than the critical angle will propagate in this layer, only able to spread its energy cylindrically, the energy travels further so is good for long distance messaging. The basic rule of thumb is that the ray will tend to be "repelled" by higher velocity media, so if you have a high velocity boundary surrounding a low velocity tube the energy will not be able to escape.
 

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