How Does the Michelson-Morley Experiment Detect Differences in Light Speed?

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Discussion Overview

The discussion revolves around the Michelson-Morley experiment and its ability to detect differences in the speed of light through interference patterns. Participants explore the implications of phase shifts in light beams and the educational context surrounding the experiment.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant expresses confusion about how the Michelson-Morley experiment detects differences in the speeds of reflected beams.
  • Another participant explains that the beams would take different times to reach the output arm, resulting in an out-of-phase condition and a different fringe pattern.
  • It is noted that the interference pattern indicates a phase shift of the waves, which some participants relate to the velocities of the light beams.
  • A participant clarifies that a phase difference arises from different wave speeds and describes how this would manifest in the experiment.
  • One participant mentions that there is no actual phase difference observed in the experiment, suggesting that relativity is needed to explain the results, but speculates on how an interferometer would detect a speed difference if it existed.
  • There is a discussion about the educational levels of participants, with references to "A level" and "B level" indicating the depth of explanation desired.
  • A participant provides a link to an external resource aimed at laymen, suggesting it may be helpful for understanding the experiment.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the relationship between interference patterns and light speeds. There is no consensus on the implications of the experiment's results, particularly concerning the existence of a phase difference.

Contextual Notes

Some participants reference educational levels and the context in which the Michelson-Morley experiment is typically taught, indicating potential variations in background knowledge among contributors.

Who May Find This Useful

Individuals interested in the Michelson-Morley experiment, its historical significance in physics, and those seeking to understand the concepts of interference patterns and phase shifts in light. This may be particularly relevant for students at secondary or early tertiary education levels.

LSMOG
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In Michaelson-Morley experiment, how woul we know if there was a difference in speeds of reflected beam. Please, I am lost.
 
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The beams would take different times to get to the output arm, so would be out of phase. You would see a different fringe pattern as a result.
 
... you would know because of the interference pattern.
What level of education are you at?
 
Simon Bridge said:
... you would know because of the interference pattern.
What level of education are you at?
Its B level, I made a mistake to choose A level.
I thought the interference patterns tells us about the phase shift of the waves, I didn, know if it has anything to do with velocities. Am I correct?
 
You get a phase difference because of the different wave speeds. Think of the wave crests traveling through the two arms. If the speed of light is different then two wave crests leaving the beam splitter at the same time take different amounts of time to travel the same distance, so return at different times. That means there's a phase difference which depends on the difference in speeds along the two arms.

Actually, there is no phase difference and we have to develop relativity to explain that. But if there were a speed difference, the above is how an interferometer would detect it.
 
I'll leave Ibix to puzzle it out - check in in the morning (local time).
What does "B level" mean? To me "A level" was a UK exam for secondary school.
For "education level" please reply with highest education achieved - ie: secondary (high school) or tertiary (college) and what year (1st year, 2nd year etc).
For instance: Michealson-Morely experiment may be encountered, in NZ, in senior secondary school (year 11 or 12, ie 16-18yo) or in the 1st 2 years of University.
I'm puzzled because you have asked, in another thread, about how things get to have a colour - which would normally be covered, in NZ, in year 8 or 9 science classes (ie 13-14 yo students).
 
Simon Bridge said:
What does "B level" mean? To me "A level" was a UK exam for secondary school.
This refers to the PF thread levels. We allow the OP to specify the level of response that they would like in order to help us respond at a helpful level.

B level is "basic" it means that the OP is looking for answers at a pre-college level. Either no math or only algebra.

I level is "intermediate" it means that the OP is looking for answers at an undergraduate college level. Some simple calculus would be appropriate.

A level is "advanced" it means that the OP is looking for answers at a post-graduate college level. All advanced math is appropriate.
 
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Here is something I wrote for laymen. Maybe it will help. It helped me.

http://www.relativitysimulation.com/Documents/MichaelsonMorelyAnalogy.htm
 

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