Blackbody emission in 2D coordinates

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Discussion Overview

The discussion revolves around the adaptation of blackbody radiation concepts to a two-dimensional framework, specifically in Cartesian coordinates. Participants explore how to modify the understanding of spectral radiance and Planck's equation when considering radiation emitted from a cylindrical cross-section rather than a spherical one.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how to handle the units of spectral radiance when transitioning to a 2D problem, suggesting that the emission should be approximated from a cylinder rather than a sphere.
  • Another participant proposes that no changes are necessary and suggests thinking of the problem as "per meter of height" to simulate a 3D universe that is homogeneous in one dimension.
  • A different participant expresses confusion about the mathematical treatment of radiation due to its 3D nature, indicating a need to integrate over a great circle of a sphere to derive a cylindrical model.
  • Another participant argues against the necessity of spherical models, stating that total radiation from a surface can be considered in a solid angle of 2 pi with a uniform distribution over a single 2D angle.

Areas of Agreement / Disagreement

Participants exhibit differing views on whether modifications to the traditional understanding of blackbody radiation are necessary when applying it to a 2D context. There is no consensus on the best approach to mathematically treat the problem.

Contextual Notes

The discussion highlights the complexity of adapting 3D radiation concepts to a 2D framework, with unresolved mathematical steps and differing interpretations of how to apply Planck's equation in this context.

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The spectral radiance of a blackbody has units of W·sr-1·m-2·Hz-1. How do I deal with these units if I want to think about a 2D problem of radiation in Cartesian coordinates? I assume that instead of a sphere of emission (which would result in artificial decrease in intensity with the inverse square of the distance) I should then approximate emission from the cross-section of a cylinder. What kind of changes to Planck's equation, its units, or some other condition of its application, must be made for this?
 
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You don't need changes, you can think of everything as "per meter of height" (simulating a 3D universe that is completely homogeneous in one dimension).
 
I agree about simulating a 3D universe in which one dimension is homogeneous. However, I do not understand how to treat this mathematically because of the intrinsically 3D nature of radiation. It seems I need to find the radiation over a great circle of a sphere and then integrate in the third dimension to give a cylinder of 1 unit thickness. Otherwise, I'm not sure how to do it.
 
There is no need to make spheres, and I don't see where you try to make them.
The total radiation from a surface will be in a solid angle of 2 pi with a uniform distribution over your single 2D angle.
 

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