why do concave lens diverge rays of light and cinvex lens converge rays of light after refraction???

Question

plzzz try and answer within a hour

Answer 1

They both refract light towards the normal on entering glass, and away from normal on leaving glass.

It is the special shape of the lens that makes parallel rays converge or diverge. There's a good diagram at the link below.

Cheers,
Ben

Answer 2

You need to do a ray trace through the lens. Snell's law says that a ray of light entering a high index of refraction media from a lower one, will bend toward the normal to the surface and vice versa for light going from high to low index material. The geometry of the concave lens is such that the light diverges on exiting the lens - again you need to do the ray trace to see this clearly or get an optics book or Google it. A convex lens has a geometry such that the light converges to a point beyond the lens upon exiting the lens.

Answer 3

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 4

The path of a ray through a prism due to refraction bends towards the base of the prism.

The cross section of convex lens can be approximated to two prisms joined at the bases. [Center portion of the lens form the bases of the prisms]

The paths of rays entering the upper and lower prism are turned toward the bases of the prisms. That is to say that the rays from the upper and lower portions of the lens meet together, in other words they converge.

The cross section of concave lens can be approximated to two prisms joined at their apexes. [Center portion of the lens form the apexes of the prisms]

The paths of rays entering the upper and lower prism are turned toward the bases of the prisms. That is to say that the rays from the upper and lower portions of the lens do not meet, in other words they diverge.