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I was wondering why would light rays converge at a biconvex lens and diverge at a biconcave lens? Is it concerning on how light rays behave in a convex or a concave mirror?

Also, is it possible to predict or sketch how would light rays behave using the angle of incidence and angle of refraction?

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    $\begingroup$ Try googling by the phrase "lens as composed of prisms", and u might get a good reason. $\endgroup$ – Wrichik Basu May 14 '17 at 13:35
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    $\begingroup$ I suspect you meant biconvex and biconcave. If you truly did mean "bio" rather than "bi" as a prefix, this question is perhaps better suited for the biology SE site. $\endgroup$ – David Hammen May 14 '17 at 14:11
  • $\begingroup$ Sorry. It was indeed "bi" sorry for the typo. $\endgroup$ – Czar Luc May 14 '17 at 14:20
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Here is what I think,

At P1, By Snells law, Since the glass is a denser medium(as compared to air), the velocity of light is less than that in air. Therefore, the light ray deflects towards the normal.enter image description here

Afterwards, at P2, Since the air is a rarer medium than glass, By Snell's Law, light gets deflected away from the normal.enter image description here

In the same way you can explain that of a biconcave lens.

Hope this helps :)

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  • $\begingroup$ How did you know how the normal lines are oriented at each point? I actually thought about your answer but I couldn't figure out how to orient the normal lines at each point. $\endgroup$ – Czar Luc May 14 '17 at 15:36
  • $\begingroup$ The surfaces of most lenses are sections of spheres. It's possible to prove that you get better focusing if the surfaces are instead paraboloids. $\endgroup$ – rob May 14 '17 at 16:01
  • $\begingroup$ The normals are always taken perpendicular to the surface( at that point) . $\endgroup$ – Physicpsycho May 14 '17 at 17:03
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You can show it using Snell's law of refraction, or the least time principle. However, this is not similar to convex or concave mirrors.

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