How to calculate transmissivity of a set of reflective foils

Click For Summary

Discussion Overview

The discussion revolves around calculating the transmissivity of a series of reflective foils, particularly focusing on the behavior of radiation as it interacts with these foils. The conversation includes theoretical considerations about absorption, reflection, and re-emission of radiation, as well as the implications of the physical properties of the materials involved.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant proposes that an infinitely thin foil absorbs 1% of incoming radiation and emits 0.5% in both directions, suggesting a transmission of 0.5% for the first foil.
  • Another participant questions the fate of the remaining 99% of the radiation after the first foil, noting that reflection depends on the dielectric constant of the foil and referencing Fresnel Equations.
  • A different participant asserts that since the foil is a conductor (specifically gold), it reflects 99% of the radiation and emits an additional 0.5% in one direction.
  • Some participants challenge the concept of an "infinitely thin" foil, arguing that a sufficiently thin gold foil would allow significant light transmission and questioning the thickness implied in the original scenario.
  • One participant emphasizes that all light is either reflected or absorbed, with absorbed light being emitted equally in both directions, reiterating the assumption of an infinitely thin foil to ignore side emissions.
  • Another participant raises concerns about the relevance of transmitted light and suggests that absorbed light will warm the material, complicating the re-emission process and indicating a need for additional parameters in the model.

Areas of Agreement / Disagreement

Participants express differing views on the assumptions regarding the thickness of the foil and the treatment of transmitted light. There is no consensus on the model or the implications of absorption and reflection, indicating ongoing debate and uncertainty.

Contextual Notes

Limitations include assumptions about the foil's thickness, the treatment of absorbed light, and the dependence on material properties like the dielectric constant. The discussion does not resolve these complexities.

Christofer Br
Messages
51
Reaction score
0
Suppose I have an infinitely thin foil that absorbs 1% of incoming radiation. It therefore emits 0.5% of the incoming radiation in both directions perpendicular to the plane of the foil. That is, transmission is 0.5%. How to calculate transmission for a series of such foils? There will be a lot of absorption and reemission between the layers and I don't know how to integrate all of this
 
Science news on Phys.org
Christofer Br said:
That is, transmission is 0.5%
I am wondering what happens to the remaining 99% of the radiation after the first foil in your thought experiment. The reflection will depend on the Dielectric constant of the foil. See this link on Fresnel Equations.
 
sophiecentaur said:
I am wondering what happens to the remaining 99% of the radiation after the first foil in your thought experiment. The reflection will depend on the Dielectric constant of the foil. See this link on Fresnel Equations.
It will be reflected, the foil is a conductor (lets assume it's gold because it has relatively constant emissivity across a very broad spectrum, exact properties are not important) - so it REFLECTED 99% and emitted additional 0.5% in one direction
 
Last edited:
An "infinitely thin" foil is a bit too much of an abstraction for this question. Loads of light will pass through a thin enough gold foil. Just how thick are you suggesting?
 
sophiecentaur said:
An "infinitely thin" foil is a bit too much of an abstraction for this question. Loads of light will pass through a thin enough gold foil. Just how thick are you suggesting?
Just consider that all the light is either reflected or absorbed, and the absorbed light is immediately emitted equally in both directions perpendicular to the plane of the foil (thats why I insisted on an infinitely thin foil, so we can ignore emmisions from the "sides")
 
Christofer Br said:
Just consider that all the light is either reflected or absorbed, and the absorbed light is immediately emitted equally in both directions perpendicular to the plane of the foil (thats why I insisted on an infinitely thin foil, so we can ignore emmisions from the "sides")
You are assuming that the transmitted light is not relevant here then? I have a problem with that.
Also, when light is absorbed, it will warm up the material and not re emit the same optical wavelength.
I think you need to modify your model to include some extra relevant parameters if you want to obtain a relevant result.
 

Similar threads

Graduate The relationship between absorbtion, emissivity and reflection
  • · Replies 1 ·
Replies
1
Views
7K
Undergrad How do emissivity and absorptivity affect thermal imaging results?"
  • · Replies 3 ·
Replies
3
Views
4K
Graduate How do different materials interact with light?
  • · Replies 5 ·
Replies
5
Views
4K
Graduate How Can Light Transmission and Reflection Exceed 100% in an Optics Experiment?
  • · Replies 3 ·
Replies
3
Views
2K
What is the Correct Way to Calculate Emissivity and Absorptivity?
  • · Replies 8 ·
Replies
8
Views
2K
Understanding Radio Waves & Oxygen Absorption at 60GHz
  • · Replies 1 ·
Replies
1
Views
2K
Graduate Understanding conceptually how a plane wave interacts with a boundary
  • · Replies 3 ·
Replies
3
Views
2K
Graduate Calculating Reflective coefficient for glass slab
  • · Replies 2 ·
Replies
2
Views
3K
Graduate How can we explain continuous absorption / emission?
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad Can a Photon be Absorbed Without the Exact Energy Level?
  • · Replies 36 ·
2
Replies
36
Views
11K