0
$\begingroup$

I am not asking for too many experimental details. Just give me a rough idea of what things could one measure using which instruments so that the ultraviolet catastrophe (Rayleigh-Jeans law) could be refuted. Also, how does one experimentally verify the Planck's radiation spectrum? Assume me to be a senior undergraduate while explaining things.

$\endgroup$
5
  • $\begingroup$ Umm... your eyeballs with an object that's hot? Infinite energy emission is a problem. $\endgroup$
    – user121330
    Commented Oct 27, 2017 at 1:21
  • 1
    $\begingroup$ So ... the thing here is that the prediction is so outrageous that it was refuted before it was ever made, There are at least three classes of measurements that come to mind and any of them could be done multiple ways. $\endgroup$ Commented Oct 27, 2017 at 1:24
  • $\begingroup$ @user121330 I have just expanded my question about Planck's law. Can you please reply? $\endgroup$ Commented Oct 27, 2017 at 1:27
  • 1
    $\begingroup$ "How can one experimentally refute the ultraviolet catastrophe" - it's called a catastrophe for a good reason. When such seemingly reasonable scientific principles unambiguously lead to a nonsense result, that a black body in thermal equilibrium at finite temperature radiates 'infinite' power, there's no question of experimental refutation. That fact that we exist refutes it thus. $\endgroup$ Commented Oct 27, 2017 at 2:55
  • $\begingroup$ @Bingo Ask a new question. It's a little rude to pull the rug out from under the people who've already answered. $\endgroup$
    – user121330
    Commented Oct 27, 2017 at 17:32

1 Answer 1

4
$\begingroup$

No instruments required. Turn on a light bulb and note that everything around it does not catch fire, vaporize, or turn cancerous. According to the Raleigh-Jeans law, an object with greater than zero temperature should emit more power at higher frequency light. However much power is emitted as visible light, more power should be emitted as ultraviolet light, still more as X-rays, and on and on. This leads to an infinite amount of power being radiated from all objects that are hotter than absolute zero. Obviously, this does not happen.

As for measuring the real spectrum of black bodies, it's a matter of separating the different wavelengths of light and using a photometer or photodiode to measure the power of each. The separation can be done with a diffraction grating and the measurements done at different angles, or with series of narrowband filters.

$\endgroup$
3
  • $\begingroup$ Thanks, @Mark H I have expanded my question to verify Planck's radiation law. Do you have anything to say about it. $\endgroup$ Commented Oct 27, 2017 at 1:26
  • $\begingroup$ @Bingo Answer updated. $\endgroup$
    – Mark H
    Commented Oct 27, 2017 at 2:05
  • $\begingroup$ for experiments , there are a lot if one googles example :phys.ksu.edu/personal/rprice/BB.pdf $\endgroup$
    – anna v
    Commented Oct 27, 2017 at 3:33

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.