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Which statement is true?

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  1. Feb 15, 2015 #1
    1. The problem statement, all variables and given/known data
    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.


    2. Relevant equations
    none

    3. The attempt at a solution
    Choice 1 is wrong, choice 2 appears to be right, choice 4 also seems right. Choice 3 is wrong
     
  2. jcsd
  3. Feb 15, 2015 #2

    phinds

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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.
     
  4. Feb 15, 2015 #3
    For choice 2, as you heat an object, its wavelength becomes shorter i.e. less in infrared more in visible no?
     
  5. Feb 15, 2015 #4

    phinds

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    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
     
  6. Feb 15, 2015 #5
    Yes, but if it is at the range where it is about to be visible light, then wouldn't the statement be true?
     
  7. Feb 15, 2015 #6

    vela

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  8. Feb 15, 2015 #7

    phinds

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    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.
     
  9. Feb 15, 2015 #8
    No thats not my point of view I was just examining all possibilities because I dont know what the answer is but ok
     
  10. Feb 15, 2015 #9

    vela

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    You seem to be assuming the total amount of light radiated is constant with temperature. It's not.
     
  11. Feb 15, 2015 #10
    Doesn't it increase with temperature?
     
  12. Feb 15, 2015 #11

    vela

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    Yes. Did you look at the plots of the blackbody spectrum at different temperatures? Does the amount of IR radiation decrease with rising temperature?
     
  13. Feb 15, 2015 #12
    nope it rises
     
  14. Feb 15, 2015 #13

    phinds

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    And what do you conclude from this, as regards your problem?
     
  15. Feb 15, 2015 #14
    I guess answer 4 is correct despite its ambiguity
     
  16. Feb 15, 2015 #15

    phinds

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    Uh ... we were talking about question #2
     
  17. Feb 15, 2015 #16
    yep answer 2 must be false then from the black body spectrum
     
  18. Feb 15, 2015 #17

    phinds

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    Good. Now you see why I suggested you might want to rethink your original answer.
     
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