Difference between optical and geometrical length in optical path

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Discussion Overview

The discussion centers around the difference between optical length and geometrical length in the context of optical path. Participants explore definitions, calculations, and implications of these concepts in geometrical optics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant seeks clarification on the difference between optical length and geometrical length in optical paths.
  • Another participant suggests that "optical length" likely refers to "optical path length," defined as the product of geometric length and the refractive index of the medium.
  • A participant provides an example comparing optical path lengths in water and glass, noting that both can have the same geometrical length but different optical path lengths due to differing refractive indices.
  • One participant expresses confusion about the existence of "optical length" and seeks clarification on how to calculate both optical path length and geometrical path length.
  • Another participant reiterates that optical path length is calculated as the distance light travels multiplied by the refractive index, emphasizing its importance for determining the phase of light.
  • A repeated explanation of the formula for optical path length is provided, reinforcing the relationship between optical path length, geometrical path length, and refractive index.

Areas of Agreement / Disagreement

Participants generally agree on the definitions and calculations of optical path length and geometrical length, but there is some uncertainty regarding the term "optical length" and its implications.

Contextual Notes

Some participants express confusion about terminology and the context of the original question, indicating potential limitations in understanding or definitions used.

deni
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I'm searching for a week from now and can't find out difference between optical and geometrical length in optical path.
Can anyone explain or give me idea or how can I find it out?
 
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After looking around a bit, it appears that the "optical length" means the "optical path length", which is the product of the geometric length (the physical distance the light travels) and the refractive index of the medium.

For example, if light travels through 10 cm of water with a refractive index of 1.33 it will have traveled along a shorter optical path than light which travels through 10 cm of glass with a refractive index of 1.5, even though both have the same geometrical length.

Sources:
http://en.wikipedia.org/wiki/Optical_path_length
http://scienceworld.wolfram.com/physics/OpticalPathLength.html
 
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I agree that "optical path length" is probably what you're looking for. If you can give us a link to where you saw "optical length", or a brief quote if it wasn't on a web page, we can see the context and make sure about this.
 
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The content wasn't in English so this was the reason why I haven't posted reference.
I have learned Geometrical Optics but still I can't understand completely the question.

The question exactly was: What is difference between optical and geometrical length of optic path?

Now I'm really confused. So yes light speed depends on the medium but there really exist optical length or not!

How to calculate "optical path length" and how to calculate "geometrical path length"!
 
The optical path length is simply the distance the light travels times the refractive index. For example, light traveling through 10 cm of water has an optical path length of 10 x 1.333 or 13.3 cm. The geometric length is simply the physical distance the light travels.

The optical path length is important because it allows us to find out what the phase of the light will be at any point, whereas the geometrical length doesn't.
 
Drakkith said:
The optical path length is simply the distance the light travels times the refractive index. For example, light traveling through 10 cm of water has an optical path length of 10 x 1.333 or 13.3 cm. The geometric length is simply the physical distance the light travels.

The optical path length is important because it allows us to find out what the phase of the light will be at any point, whereas the geometrical length doesn't.

c1 = n * c2

where: c1 - optical path length , c2 - geometrical path length and n - refreactive index

Thank you a lot this is exactly what I was searching for.
 
Last edited:

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