The Naked Scientists

The Naked Scientists Forum

Author Topic: How was radiation frequency measured in the year 1900?  (Read 4007 times)

Offline PAOLO137

  • Jr. Member
  • **
  • Posts: 32
    • View Profile
When Max Plank and others were trying to find the right equation relating the temperature of a black body and the frequencies of the electromagnetic radiation inside, how did they manage to measure the frequencies with the experimental means available at that time?
Edit: Changed the title to a question.
« Last Edit: 30/03/2015 20:48:17 by evan_au »


 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4109
  • Thanked: 245 times
    • View Profile
Re: How was radiation frequency measured in the year 1900?
« Reply #1 on: 30/03/2015 20:52:48 »
As early as 1859, Gustav Kirchoff was using the spectrum of light to look at the wavelengths emitted by hot objects.
 

Offline chiralSPO

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 1873
  • Thanked: 143 times
    • View Profile
Re: How was radiation frequency measured in the year 1900?
« Reply #2 on: 30/03/2015 22:46:24 »
Double slit diffraction was one method available to them. I don't know the extent to which it was used, but they had the math worked out so they could calculate wavelengths with fairly high precision. Interferometers were also important tools.
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2760
  • Thanked: 38 times
    • View Profile
Re: How was radiation frequency measured in the year 1900?
« Reply #3 on: 31/03/2015 03:21:29 »
When Max Plank and others were trying to find the right equation relating the temperature of a black body and the frequencies of the electromagnetic radiation inside, how did they manage to measure the frequencies with the experimental means available at that time?
Edit: Changed the title to a question.
That depends on the wavelengths which they were trying to observe. Different wavelengths require different methods of observation.
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8655
  • Thanked: 42 times
    • View Profile
Re: How was radiation frequency measured in the year 1900?
« Reply #4 on: 03/04/2015 17:28:26 »
To be fair, they probably didn't measure the frequency, they calculated it from the wavelength.
 

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4704
  • Thanked: 153 times
  • life is too short to drink instant coffee
    • View Profile
Re: How was radiation frequency measured in the year 1900?
« Reply #5 on: 03/04/2015 19:29:50 »
If you look up "ultraviolet catastrophe" in Wikipedia you will see that Planck's equation was in fact a purely theoretical response to a logical absurdity in classical statistical mechanics. It turned out that the stroke of genius in invoking discrete quanta to dispel the anomaly, actually explained the observed photoelectric effect.

Thus the black body spectrum did not require precise experimental determination - the photoelectric effect is a lot easier to measure accurately, and can be explored up to x-ray energies, where the tail of the black body spectrum turns out to be exactly as predicted.
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2760
  • Thanked: 38 times
    • View Profile
Re: How was radiation frequency measured in the year 1900?
« Reply #6 on: 03/04/2015 21:15:31 »
Quote from: alancalverd
It turned out that the stroke of genius in invoking discrete quanta to dispel the anomaly, actually explained the observed photoelectric effect.
This seems to be a common misconception. It wasn't Planck himself that quantized radiation. That hypothesis is due to Einstein. What Planck did was to quantize the wall oscillators that make up the black body so that the energy was quantized. That didn't mean that radiation was quantized since theoretically other sources could radiate energy which wasn't quantized in that fashion. This is a very subtle point.

See: http://en.wikipedia.org/wiki/Black-body_radiation
Quote
Planck had to assume that the energy of the oscillators in the cavity was quantized, i.e., it existed in integer multiples of some quantity. Einstein built on this idea and proposed the quantization of electromagnetic radiation itself in 1905 to explain the photoelectric effect.

See also: http://galileo.phys.virginia.edu/classes/252/PlanckStory.pdf
Quote
Incidentally, it didnít occur to him that the radiation itself might be in quanta: he saw this quantization purely as a property of the wall oscillators.

This seems to be getting a tad off topic.
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11993
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Re: How was radiation frequency measured in the year 1900?
« Reply #7 on: 15/04/2015 23:03:14 »
I think Planck was really brilliant, where he might have hesitated was, very tentatively, in the way he wanted to fit his mathematics, and ideas, with the then expected definitions of science, Planck scale is one of the absolutely coolest ideas Ive read about, and if right worth at least worth a Nobel Prize, maybe more :) But he didn't get one from that idea, just as Einsteins relativity never got a Nobel Prize either.
 

Offline PAOLO137

  • Jr. Member
  • **
  • Posts: 32
    • View Profile
Re: How was radiation frequency measured in the year 1900?
« Reply #8 on: 29/04/2015 11:32:04 »
Many thanks to all the people that have given an answer. I am satisfied to know that at that time there were enough
technical methods to perform such measurement. Paolo.
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2760
  • Thanked: 38 times
    • View Profile
Re: How was radiation frequency measured in the year 1900?
« Reply #9 on: 29/04/2015 15:13:34 »
Many thanks to all the people that have given an answer. I am satisfied to know that at that time there were enough
technical methods to perform such measurement. Paolo.
I'm curious. May I ask you what led you to question whether it was true or not?
 

The Naked Scientists Forum

Re: How was radiation frequency measured in the year 1900?
« Reply #9 on: 29/04/2015 15:13:34 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length