Understanding the Infrared Glow of Objects: Hotter is Not Always Brighter

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Discussion Overview

The discussion revolves around the relationship between temperature and the infrared glow of objects, particularly in the context of a homework question. Participants explore concepts related to thermal radiation, blackbody spectra, and the implications of temperature on the wavelengths of emitted radiation.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • Some participants argue that the color an object glows is related to its temperature, while others question the phrasing of the homework question regarding infrared and visible light.
  • There is a discussion about whether the day side of the Earth glows brighter in the infrared compared to the night side, with some suggesting that the question is poorly worded.
  • One participant points out that as an object heats up, it emits radiation in a range of infrared wavelengths before becoming visible, challenging the binary view of infrared radiation.
  • Another participant suggests comparing the spectra of blackbodies at different temperatures to understand the relationship between temperature and emitted radiation.
  • There is a contention regarding whether the total amount of light radiated remains constant with temperature, with some asserting that it increases with temperature.
  • Participants express uncertainty about the implications of their findings on the original homework question, leading to further debate about the correctness of specific answer choices.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correctness of the statements in the homework question. Multiple competing views and interpretations remain, particularly regarding the relationship between temperature, infrared radiation, and visible light.

Contextual Notes

Participants highlight ambiguities in the homework question and the need for clarity regarding the definitions of terms like "infrared" and "visible." There are also unresolved discussions about the implications of blackbody radiation and how it relates to the statements in the question.

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Homework Statement


Which statement is true?
The color an object glows has nothing to do with how hot it is.

As you heat an object, it glows more in the visible and less in the infrared.

The day side of the Earth reflects more light, but the night side glows brighter in the infrared.

You glow brighter in every wave length than a frozen body would.

Homework Equations


none

The Attempt at a Solution


Choice 1 is wrong, choice 2 appears to be right, choice 4 also seems right. Choice 3 is wrong
 
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Science is not a democracy and "voting" for the right answers is ridiculous so a poll is not a good idea.

#1 I agree it's wrong
#2 You might want to this think through again
#3 Well since the day side GETS more light, I'd say, yeah, it reflects more light, but is that a property of the day side or a property of the incident light? I think the question is a poor one. In any case, do you think the day side glows brighter in the infrared? Is that why you consider this one wrong? (I would agree, by the way)
#4 if we're only talking about radiation as opposed to reflection I agree w/ you but it seems like another ambiguously worded question.
 
phinds said:
Science is not a democracy and "voting" for the right answers is ridiculous so a poll is not a good idea.

#1 I agree it's wrong
#2 You might want to this think through again
#3 Well since the day side GETS more light, I'd say, yeah, it reflects more light, but is that a property of the day side or a property of the incident light? I think the question is a poor one. In any case, do you think the day side glows brighter in the infrared? Is that why you consider this one wrong? (I would agree, by the way)
#4 if we're only talking about radiation as opposed to reflection I agree w/ you but it seems like another ambiguously worded question.
For choice 2, as you heat an object, its wavelength becomes shorter i.e. less in infrared more in visible no?
 
Perhaps you think "in the infrared / not in the infrared" is pure binary? Actually there is quite a range of infrared and as you heat up an object it moves TOWARDS the visible but until it starts to glow (faint orange) it isn't there yet and will be radiating more strongly but still in infrared, just in shorter wavelengths
 
phinds said:
Perhaps you think "in the infrared / not in the infrared" is pure binary? Actually there is quite a range of infrared and as you heat up an object it moves TOWARDS the visible but until it starts to glow (faint orange) it isn't there yet and will be radiating more strongly but still in infrared, just in shorter wavelengths
Yes, but if it is at the range where it is about to be visible light, then wouldn't the statement be true?
 
shmijda said:
Yes, but if it is at the range where it is about to be visible light, then wouldn't the statement be true?
So your point of view is "eh ... it COULD be true. If I set up things just right, there might be a special case where it's true. SO ... by me, it's true. End of story"

Sounds more like a negotiation than a search for reality.
 
phinds said:
So your point of view is "eh ... it COULD be true. If I set up things just right, there might be a special case where it's true. SO ... by me, it's true. End of story"

Sounds more like a negotiation than a search for reality.
No that's not my point of view I was just examining all possibilities because I don't know what the answer is but ok
 
shmijda said:
Yes, but if it is at the range where it is about to be visible light, then wouldn't the statement be true?
You seem to be assuming the total amount of light radiated is constant with temperature. It's not.
 
  • #10
vela said:
You seem to be assuming the total amount of light radiated is constant with temperature. It's not.
Doesn't it increase with temperature?
 
  • #11
Yes. Did you look at the plots of the blackbody spectrum at different temperatures? Does the amount of IR radiation decrease with rising temperature?
 
  • #12
vela said:
Yes. Did you look at the plots of the blackbody spectrum at different temperatures? Does the amount of IR radiation decrease with rising temperature?
nope it rises
 
  • #13
shmijda said:
nope it rises
And what do you conclude from this, as regards your problem?
 
  • #14
phinds said:
And what do you conclude from this, as regards your problem?
I guess answer 4 is correct despite its ambiguity
 
  • #15
shmijda said:
I guess answer 4 is correct despite its ambiguity
Uh ... we were talking about question #2
 
  • #16
phinds said:
Uh ... we were talking about question #2
yep answer 2 must be false then from the black body spectrum
 
  • #17
shmijda said:
yep answer 2 must be false then from the black body spectrum
Good. Now you see why I suggested you might want to rethink your original answer.
 

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