Light: same frequency=different wavelength?

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    Light Wavelength
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Discussion Overview

The discussion centers around the behavior of light waves as they transition between different mediums, specifically addressing the relationship between frequency, wavelength, and the speed of light. Participants explore the implications of the refractive index and the challenges of measuring light's speed in various environments.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions why light waves maintain the same frequency when passing through different mediums while exhibiting different wavelengths, suggesting a need for clarification on the relationship between frequency, speed, and wavelength.
  • Another participant confirms that the speed of light changes in different mediums, introducing the concept of the refractive index.
  • A participant shares an anecdote from a physics teacher regarding the measurement of light's speed in water versus air, questioning the meaning of "easier" in this context and suggesting it might relate to accuracy in measurements.
  • Further elaboration is provided on the challenges of measuring speed in different mediums, with one participant arguing that measuring in air may be less complicated than in water due to potential errors introduced by dispersion.
  • Another participant discusses the accuracy of measuring the speed of light in vacuum compared to other mediums, noting that the standard unit of distance is defined based on light's travel in vacuum, implying that measuring speed in water is not preferred for defining distance.

Areas of Agreement / Disagreement

Participants express differing views on the implications of measuring light's speed in various mediums, particularly regarding the concept of "easier" measurements and the accuracy of such measurements. No consensus is reached on the best approach or understanding of these concepts.

Contextual Notes

Participants mention various assumptions regarding the definitions of refractive index and measurement accuracy, as well as the potential for dispersion to affect measurements, but these aspects remain unresolved.

LLT71
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can someone explain why light waves have the same frequency when they pass through different mediums, and at a same time they have different wavelenghts? if frequency=speed of light (which is constant I assume) /wavelength, how could it be? does the speed of light somehow changes when light passes different mediums to get the same result or?
thanks!
 
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LLT71 said:
does the speed of light somehow changes when light passes different mediums
Yes. It is usually referred to as the Refractive index (click for wikipedia page)
 
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jerromyjon said:
Yes. It is usually referred to as the Refractive index (click for wikipedia page)
thank you!
 
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Yes. To share something
told by my physics teacher, scientists can determine the speed of light relatively "easier" when it moves through a liquid medium like water compared to when it moves through air. (I think its refractive index is close to vacuum? Correct me if I'm wrong)
 
lonelypancreas said:
Yes. To share something
told by my physics teacher, scientists can determine the speed of light relatively "easier" when it moves through a liquid medium like water compared to when it moves through air. (I think its refractive index is close to vacuum? Correct me if I'm wrong)
I'm not sure what was meant by the term "easier" - possibly it referred to the possible accuracy.
To measure speed, you need to know (in one form or another) a distance and a time. The ratio of speeds in air (space) and water (or many other transparent substances) is only a factor of about 1.5. Your teacher may be implying that the error in measuring the time taken to traverse a given distance would be the same in absolute terms, so the percentage error over a longer time could be less. It's a matter of opinion whether that would be the main source of error.
Personally, I think it would be 'easier' to do an experiment in air than one involving water (slightly messier to deal with). It's also arguable that any dispersion in the medium could also introduce errors in measuring the edges of pulses.
 
On the assumption that "easier" means more accurate, our ability to measure time and the speed of light in vacuum are so good that they exceed our ability to measure distance directly. In fact our standard unit of distance is defined in terms of how far light can travel in vacuum in a certain amount of time.

If it were easier to measure speed in water, they'd have defined distance in terms of how far light can travel in water. But it isn't. And they don't.
 

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