Refractive Index: Light Speed & Distance Perception

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  • Thread starter Thread starter Ahmed Samra
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Discussion Overview

The discussion revolves around the effects of refractive indices on the perception of distance and position of objects when viewed through different media, such as glass and air. Participants explore the implications of light speed changes in various materials and how this affects visual perception, measurement, and the concept of optical path length.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants assert that light travels in a straight line in a vacuum, but its speed is reduced in media like glass and air, leading to questions about whether this affects perceived distances.
  • One participant emphasizes that distance is measured, not seen, and suggests that understanding measuring instruments is crucial for accurate distance perception.
  • Another participant raises the question of whether the refractive index of gas particles alters the perceived position of nearby objects, such as a car.
  • Some participants discuss how light refraction through different media can distort the apparent position of objects, with specific examples like viewing a fish in water from an angle.
  • A mathematical example is provided to illustrate the concept of optical path length versus real path length, indicating that the differences may be imperceptible to the human eye.

Areas of Agreement / Disagreement

Participants express varying views on the implications of refractive indices on perception. While some agree that refraction affects perceived positions, others question the extent of this effect and whether it is significant enough to be noticed. The discussion remains unresolved regarding the overall impact of these factors on visual perception.

Contextual Notes

Limitations include assumptions about the observer's position relative to objects, the precision of measuring instruments, and the specific conditions under which light travels through different media. The discussion does not resolve the complexities involved in these measurements.

Ahmed Samra
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The light travel by it's in a straight line in vacuum, but when we see through the glass the glass has a refractive index which slows down the speed of light so when I see through the glass I don't see the actual distance. Moreover, the gases particles has refractive index and slows down the speed of light. Does this mean that I don't see the actual distance?
 
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By it's actual speed
 
A post and a correction one minute apart? Dude... learn to use that edit button... or check your post a few times before you submit it.
 
I am really sorry, but can you answer my question?
 
Ahmed Samra said:
The light travel by it's in a straight line in vacuum, but when we see through the glass the glass has a refractive index which slows down the speed of light so when I see through the glass I don't see the actual distance. Moreover, the gases particles has refractive index and slows down the speed of light. Does this mean that I don't see the actual distance?

You don't ever "see" a distance, you measure it, and you have to understand the operation of your measuring instruments to know what your measurements are telling you and whether they might be introducing errors that must be corrected for. If you're measuring the distance to an object using a light signal (the the radar method) that passes through a pane of glass, you have to allow for the signal needing a bit more time to pass through the glass.
 
I mean when I there is a car front of me I don't see it's real position because of the refractive index of the gas particles that slows down the speed of light?
 
Ahmed Samra said:
I mean when I there is a car front of me I don't see it's real position because of the refractive index of the gas particles that slows down the speed of light?

If the refractive medium is set up to change the course of the light, then yes of course you have to allow for this effect when deciding where the car was when the light left it on the way to your eyes.
 
Does the gas particles change the course of light?
 
That is why the sky is blue, same with a prism, all matter that light travels through even gas will distort the direction of the light until it exits. Away from the normal.
 
  • #10
So everything I seeks not in its actual position?
 
  • #11
Ahmed Samra, please read your Private Messages. You can find them at the top right corner of your screen.
 
  • #12
I don't see anything in its actual position?
 
  • #13
Ahmed Samra said:
I don't see anything in its actual position?

Unless you are standing perpendicular to the plane of entry and the light enters the plane at a 90 degree angle no. For example, If your on Earth and the sun cast no shadow (90 degrees with you) then it is where it appears to be. If you stand directly over a fish in a pond it is where it seems to be, If you look at the fish from an angle the light has refracted and it is not where it appears to be. If you are looking through any medium at an angle there will be a slight refraction of the light. Minuscule but still there.
 
  • #14
Yes, light refracts through the atmosphere.

Try looking at http://www.math.ubc.ca/~cass/courses/m309-03a/m309-projects/grant/atmoptics.html

in particular

refract22.jpg
 
  • #15
Ahmed Samra said:
The light travel by it's in a straight line in vacuum, but when we see through the glass the glass has a refractive index which slows down the speed of light so when I see through the glass I don't see the actual distance. Moreover, the gases particles has refractive index and slows down the speed of light. Does this mean that I don't see the actual distance?
I think what you are looking for is "optical path length" vs real path length.
The difference between the two for a car windshield would not be resolvable
with your measuring instrument(your eye).
And distance would be relative to what you have always seen (no delta)
Lets use the car example.
A car is 30 meters in front of you,
Now let's add in the delay of 4 mm of glass at an index of 1.5.
4 mm of glass has an optical path length of 6 mm, or +2mm
and the delay of the air at 1.000023
30 m X 1.000023= 30.00069 m.
So the true distance vs the optical distance is a Delta of 2.69 mm.
Add to this the delays look normal, as it is what we have always seen.
 

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