physics continued

The human eye alters its shape eg thick to give short focal length (high power) this ability of the high to see objects clearly at diff dist= accomodation, most refraction takes place at boundarybetween the air and the cornea becaude this is where the largest n occurs. The rays are refracted by the eye so they meet on retina to form a sharp image. The light from near pt reaches as diverging rays. 

Myopia; short sighted means what it says he is shortsighted he is unable to see distant objects sharply. They cant make the lens thin enough to view dist objects. So light from didt objects converges at a pt infront of the retina. The image seen by the person is blurred. The persons far pt is much closer to the eye than the normal infinite dist. To correct a concave lens is used with a fical length if which is equal to the persons actual far pt. This means the parallel rays of light are refracted so they appear to diverge from the persons far pt.

Long sighted; ciliary muscles are too weak to make lens thick for short focal length. 

Rays of light arent bent sufficiently to form an image on the retina. Convex lens is used to correct.

Principal of superposition;

When 2 or more waves meet(same tine and place) the resultant displacement at any pt is equal…