What Light Source Was Used in the Michelson-Morley Experiment?

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Discussion Overview

The discussion centers on the type of light source used in the Michelson-Morley experiment, exploring the characteristics required for effective interference in the context of historical experimental physics.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions the type of coherent light source used, noting that many explanations omit this detail.
  • Another participant argues that a coherent light source was not necessary, suggesting that a narrow beam would suffice.
  • A different viewpoint emphasizes the importance of having a light source with a limited range of frequencies to prevent interference effects from canceling each other out, mentioning that an oil lamp may not be suitable due to its broad frequency range.
  • One participant expresses uncertainty about the specific light source but indicates that the concern regarding frequency range did not appear to be an issue in the experiment.
  • Another participant proposes that a monochromatic light source, such as a gas discharge tube emitting a line spectrum, would be appropriate.
  • A later reply states that a carbide bicycle lamp was used, along with a sodium-vapor lamp for setup purposes.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of coherence in the light source and the implications of frequency range on the experiment's outcomes. No consensus is reached regarding the specific light source used.

Contextual Notes

Some discussions involve assumptions about the nature of light sources and their effects on interference patterns, which remain unresolved.

ZLBilley
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Since this experiment was done long before lasers were invented, what did they use as a coherent light source? All the explanations of the experiment I can seem to find skip this detail and I am curious.
 
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They didn't need a coherent light source. A narrow beam sufficed.
 
I suppose the important bit wouldn't be the coherent bit, but having a light source with a limited range of frequencies so that the change in intensity due to the change in interference in one wavelength wasn't canceled out by an opposite change in intensity from other wavelengths interfering differently. A light source like an oil lamp would have too large a range of frequencies for the interference effects to not wash each other out wouldn't it?
 
I don't know what they used as a light source, but whatever they used, the problem you raised didn't seem to be an issue.
 
For monchromatic light something like a gas discharge tube that emits a line spectrum would do the job.
 
They used a carbide bicycle lamp for the experiments. They sometimes used a sodium-vapor lamp to help set up.
 

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