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sk381
Feb24-04, 05:32 PM
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
Integral
Feb24-04, 05:54 PM
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.
sk381
Feb24-04, 08:31 PM
I am still not clear..
Can you explain more in detail..?

Thanks
Integral
Feb24-04, 08:37 PM
Do you understand the meaning of Normal in this usage?
sk381
Feb25-04, 02:47 PM
yes.. I think you mean the line perpendicular to the surface of the convex and parallel to the direction that the ray is travelling in..right/
Njorl
Feb25-04, 02:53 PM
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
Integral
Feb25-04, 03:53 PM
As Norjl said, because the Normal is pointing in a different direction at the exit point.