Optics

[nkafeel]

I am confused with this concept, so as the index of refraction increases for a medium, the angle then bends more towards the normal according to snells law. Does that mean it bends less in a higher index of refraction since the angle to normal decreases?

if you have a lens with a greater index of refraction, light bends more and your focal length decreases. Does this bending have anything to do with snell law and away or towards normal? Also dont understand what it means that "focal length decreasing" when lights bends more due to a thicker lens.

Thank you for your time.

---

Members don't see this ad.

 

[DrknoSDN]

I am confused with this concept, so as the index of refraction increases for a medium, the angle then bends more towards the normal according to snells law. Does that mean it bends less in a higher index of refraction since the angle to normal decreases?

if you have a lens with a greater index of refraction, light bends more and your focal length decreases. Does this bending have anything to do with snell law and away or towards normal? Also dont understand what it means that "focal length decreasing" when lights bends more due to a thicker lens.

Thank you for your time.

Two different topics. With snells law you are usually assuming the first medium is air (index of 1) so if you go into a new medium at 45 degrees, a new medium with refractive index 1.5 will bend it more towards normal than if the new medium only had a index of 1.3... (1.5 > 1.3 so it would bend more towards normal)

If the same light (45 degrees) was already in glass with an index of 1.5 and it then exited the glass and entered air (index 1.0) then the light would be away from normal.

Third, if you have light inside a glass with high index of refraction (1.8 or so), and it hit the wall of the glass at a low angle (shallow impact like skipping a rock on a lake), the net result is that going from the 1.8 glass to 1.0 air would not allow the light to exit because the calculation would be over 90 degrees and would result in total internal reflection.

============

With lenses you are going from air to glass to air so the index is not as significant as the curvature of the lens. If you have a lens that is completely flat on both sides it would not bend light significantly no matter what the index is (almost like looking through a window)

If you have two lenses then the thicker lens would bend light more due to the angle the light is striking the lens and cause it to have a shorter focal length.

If you had two equally thick lenses then the index of refraction would only matter qualitatively. They would not ask to calculate the difference or anything. The higher index material would amplify the bending of light more so it would have a slightly shorter focal length.