Why do light rays bend towards the center after exiting a convex lens?

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    Convex Lenses
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Discussion Overview

The discussion revolves around the behavior of light rays as they pass through a convex lens, specifically focusing on why light rays continue to bend towards the center after exiting the lens. The scope includes conceptual understanding and technical explanations related to optics and refraction.

Discussion Character

  • Conceptual clarification, Technical explanation, Debate/contested

Main Points Raised

  • One participant notes that light rays bend towards the center when entering a convex lens due to refraction and questions why they continue to do so after exiting.
  • Another participant acknowledges that light rays bend away from the Normal upon exiting the lens but suggests that the direction change is influenced by the variation in optical path length through the lens.
  • A participant requests further clarification on the explanation of the bending behavior.
  • There is a question about the understanding of the term "Normal" in the context of light refraction.
  • A participant confirms their understanding of "Normal" as the line perpendicular to the surface of the lens.
  • Another participant explains that the curvature of a biconvex lens causes a second bending towards the center, contrasting with a different lens shape that would result in straightening the ray.
  • A later reply reiterates that the bending is due to the Normal pointing in a different direction at the exit point of the lens.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the bending of light rays, with some agreeing on the influence of the lens curvature and Normal direction, while others seek further clarification. The discussion remains unresolved as to the complete explanation of the phenomenon.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the behavior of light and the definitions of terms like "Normal." The mathematical steps explaining the bending are not fully explored.

sk381
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Hi,

I know that when entering a convex lens, light rays bend towards the center due to refraction. But why do they keep bending towards the center once they exit the lens? Should'nt they now bend away from the lens because they are going from a denser to a rarer medium?

Thanks

SK
 
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Yes, the light rays bend away from the Normal to the surface when exiting the lens. But the ray still has changed direction due to the variation in optical path length through the lens.
 
I am still not clear..
Can you explain more in detail..?

Thanks
 
Do you understand the meaning of Normal in this usage?
 
yes.. I think you mean the line perpendicular to the surface of the convex and parallel to the direction that the ray is traveling in..right/
 
It is because the curve switches in a biconvex lens.

If the lense were like this (( you would get a straightening of the ray.

But if it is like this () you get a second bending toward the center.

Njorl
 
As Norjl said, because the Normal is pointing in a different direction at the exit point.
 

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