Why and how does a concave lens diverge light rays?

Answer 1

because light travels in straight lines

Answer 2

The classic example is to imagine a barrel rolling down a grassy hill and then suddenly meets the sidewalk. If the barrel is rolling at 90-degrees to the sidewalk (i.e. 'normal to the sidewalk') then when it crosses from grass to sidewalk the barrel continues to roll straight, since all points of the barrel's rolling surface went from the grass to the concrete at the same time.

But, if the barrel is rolling at an angle to the sidewalk, then when it hits the interface between grass and sidewalk, the direction of the barrel with change, since the points on the barrel that touch the concrete roll faster than on the grass. So part of the barrel will have less resistance than another part, and the direction changes.

Now, keep this in mind, and understand that light travels more slowly through glass (or plastic or any other material that lenses are made out of). If the light hits the lens at an angle, parts of the wavefront will change speed and thus the direction of the light wavefront changes direction.

Finally, if the lens is carefully shaped (i.e. concave) then it will change directions of the light wavefronts on different parts of the lens and the light can be focused or unfocused, i.e. converged or diverged.

Going back to the barrel example, now imagine a long line of barrels rolling down the grass. If you wanted them to spread out when they hit the concrete (i.e. diverge) you could shape the interface between grass and concrete in such a way to do that, and it would have a concave shape.

Answer 3

when light passes frmo one substance into another along a flat surface, its is 'broken' you can see this when looking at a straw standing in a glass of water, from the sides the straw will seem to be split in two where it enters the water.

when light enters a glass plate, it is broken in one angle, and when it exits the glass place at the other side, the angle is exaclty opposite of that one where the light entered, therefor, you will not see a change.

however if the two planes throughwihch the light enters are not perpindicular to eachother. the light will be bent in a different angle when it exits than when it enters, this produces a change in direction of hte light. hollow surface, like a concave lens has, the light will be scattered in different directions, diverging away from the center of the lens (where the light will pass through in a straight line) the further out in the lens you get the more the light will be diverged.

Answer 4

For the opposite reason from my answer to your convex question. The direction of refraction, when entering the lens, is always towards perpendicular to the glass's surface. In this case, the surface is angled so that rays further from the center get greater outward (rather than inward) refraction.

Answer 5

http://en.wikipedia.org/wiki/Concave_lens#Types_of_lenses

Answer 6

by refraction.