joriki
• Member for 10 years, 5 months
• Last seen this week
• Berlin, Germany

## 28 Actions

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Well, that will teach me to vote to migrate to physics.SE :-)

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I've answered the question but also voted to migrate it to physics.SE.

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@Don: Now that you've replaced "frequency" by "wavelength" in the question, I no longer understand the question. You start out yourself by stating that a photon's energy is proportional to the frequency, not the wavelength. Then why do you wonder "where it draws the energy to adjust its wavelength"?

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I wasn't defining; I was talking about the standard usage of the expression, pointing out that this differs from your usage of it, so that this wouldn't cause any confusion. (I didn't downvote, by the way.)

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This answer is slightly misleading. What we usually call "the speed of light (in vacuum)" is a parameter in the equations of electrodynamics. This is the speed at which monochromatic electromagnetic ways propagate in a vacuum. If you superimpose different frequencies (your first link) or add matter (your second link), all sorts of interesting things can happen. One then has to define what one means by "the speed of light", e.g. a group velocity of a wave packet. The "speed of light" thus defined for complicated wave phenomena may vary, but that does't mean the fundamental parameter $c$ varies.

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@Insig: I removed the general-relativity tag; this has nothing to do with general relativity; in fact it's not even specifically related to special relativity; it's just electrodynamics and vector calculus.

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@Insig: It doesn't if you link both questions to each other to avoid duplication of efforts.

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@FrankH: Yes, that's also the one I was referring to; I found it from the FAQ you linked to.

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@FrankH: I'm sorry, I wasn't aware that you have a different homework policy here; I originally saw this question on math.SE and followed it here when it was migrated. It's rather ironic that the FAQ you linked to (or rather the meta thread that it links to) quotes an obsolete thread on meta.math.SE to argue for this policy, which is not the current math.SE policy on homework (which is basically that everyone deals with it as they see fit).