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Black body spectrum


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Just reading a little on this and the following question was asked:

If you heated a metal ball, it would go from dull red to orange white, to yellow white to white. Why?

The answer in the textbook says as its heated, it's wavelengths will be shortened as seen in the graph (a typical graph for black body spectra). But I don't see it. Don't see why it goes red to blue when heated, why not the other way? Obviously missing something :-/

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Don't see why it goes red to blue when heated, why not the other way? Obviously missing something :-/

We call blue a "cool" colour and red a "warm" one, but that's got nothing to do with physics, more to do with our perceptions of snow, fire etc.

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We call blue a "cool" colour and red a "warm" one, but that's got nothing to do with physics, more to do with our perceptions of snow, fire etc.

Yeah I get that. Just wondered what the science behind something having a shorter wavelength when heated was. In fact it doesn't really answer that. The text just says that that's the way it is.

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 Just wondered what the science behind something having a shorter wavelength when heated was

Simplistically;

Hotter == more energy == more likelihood of producing more energetic photons == shorter 'average' emission wavelength (the shorter the wavelength, the more energy the photon has; e.g. ultraviolet vs infrared)

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A common astronomy-related question: "Why are there no green stars"? ;)

http://nogreenstars.blogspot.co.uk/2013/03/why-are-there-no-green-stars.html

(Review article containing a number of interesting links)

That is a brilliant link and has answered questions I've had in the back of my mind for years. It merits a thread in the imaging section, too. Thanks Chris.

mrjaffa, you've come across Wien's Dislacement Curve? That's worth a Google as well.

Olly

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That is a brilliant link and has answered questions I've had in the back of my mind for years. It merits a thread in the imaging section, too. Thanks Chris.

mrjaffa, you've come across Wien's Dislacement Curve? That's worth a Google as well.

Olly

Yeah that was in the text book I'm reading from :-)
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