Question

3.) Your friend Suzy complains that the writing on the board in class doesn't seem to be as sharp and clear as it used to be Suzy says she has no problem reading the text book, but once you get as far away as the board was about 4 meters it starts to get blurry.

a.) what are the ideal values for near and far points for normal human vision?

b.) is the distance of 4 meters given above Suzy's actual near or far point? is Suzy myopic or hyperopic? explain.

c.) without calculations yet would you expect Suzy to need a converging or a diverging lense?, explain answer in terms of object / image distances.

d.) once Suzy gets her glasses what focal length do you expect to find in Suzy's glasses?

e.) what prescription do you expect for Suzy's glasses?

Answer 1

a) The ideal values for near point for normal human vision is D=25 cm and for far point is infinity.

b)The distance of 4m given above is Suzy's far point.Thus Suzy is myopic since her far point is not at infinity but nearer to the eye.

c)Suzy needs a diverging lens to correct her vision for by using this lens rays coming from infinity can be made to focus on the retina of the eye since we know that for a diverging lens rays coming from infinity seem to diverge from a point closer than infinity.

d)Since rays coming from infinity seem to diverge from the focus of the lens thus by choosing the focal length of the lens to be equal to the far point distance of the eye, Suzy's vision can be corrected.

e) The prescription for Suzy's glasses includes all the above data.