Can a black material reflect light when heated to incandescence?

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Discussion Overview

The discussion centers on the behavior of black materials when heated to incandescence, specifically whether they would absorb or reflect light when illuminated. The scope includes theoretical considerations of blackbody radiation and material properties under varying temperatures.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • Some participants assert that true black materials absorb all wavelengths of visible light, while true white materials reflect all wavelengths.
  • A participant poses a question about the behavior of a black material when heated to incandescence, asking if it would absorb or reflect light when illuminated.
  • Another participant argues that even when heated, a black material continues to absorb all light, using the example of shining a flashlight on the sun to illustrate that it does not reflect light.
  • One participant reiterates the point about the sun's brightness being due to its emission rather than reflection, emphasizing that it does not reflect or scatter light from a flashlight.
  • A later reply challenges the accuracy of the sun being used as an example, suggesting that it is not a perfect blackbody and that the statement would hold true if referring to a perfect blackbody at high temperatures.

Areas of Agreement / Disagreement

Participants express differing views on the behavior of black materials when heated, with some agreeing on the absorption characteristic while others question the validity of using the sun as an example, indicating unresolved aspects of the discussion.

Contextual Notes

There are limitations regarding the definitions of "black" and "white" materials, as well as the assumptions about perfect blackbody behavior and the conditions under which these properties are discussed.

theobromine
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True black materials theoretically absorbs all wavelengths of visible light. True white materials reflect all wavelengths of light.

If a material which was black at room temperature was heated up to incandescence so that it was emitting all visible wavelengths (white light), and then light was shone at the material, would it:

a) Absorb all light, as it was black when not incandescent
or
b) Reflect all light, in essence behaving as a white object

Insight would be much appreciated!
 
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theobromine said:
Summary: True black materials theoretically absorbs all wavelengths of visible light. True white materials reflect all wavelengths of light.

What happens when a material which is ordinarily black is heated to incandescent?

If a material which was black at room temperature was heated up to incandescence so that it was emitting all visible wavelengths (white light), and then light was shone at the material, would it:

a) Absorb all light, as it was black when not incandescent
It still absorbs all light. If you shine a flashlight on the sun it does not reflect off the sun. It is brighter than your flashlight because it emits more light to the flashlight than it absorbs from the flashlight, but it does not reflect or scatter your flashlight.
 
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Dale said:
It still absorbs all light. If you shine a flashlight on the sun it does not reflect off the sun. It is brighter than your flashlight because it emits more light to the flashlight than it absorbs from the flashlight, but it does not reflect or scatter your flashlight.
Thanks, that's helpful.
 
Dale said:
If you shine a flashlight on the sun it does not reflect off the sun. It is brighter than your flashlight because it emits more light to the flashlight than it absorbs from the flashlight, but it does not reflect or scatter your flashlight.

Just a little correction: this statement is not really accurate because the sun is not a perfect blackbody. It is true if we replace the word sun with perfect blackbody at several thousand Kelvin.
 

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