Question

Problem 14 An older person wears bifocals. The lower portion of the lens is converging and has a focal length of 80 cm. The upper portion is diverging and has focal length of - 50 cm. What are near and far points of person's unaided eye? Draw separate diagram for each lens label near and far points which ever is applicable.

Answer 1

Near pomit Pa 1 closest the pornit upto which a person Corn see an abject. It is called Hybermetropia and treated by convex long. and in hypermetropia ip shifted to beyond 28cm 80 any object before the nearponit (7 mage should form near pomid. incano an object placed at a5 con should form ito virtual & erect image beyond mear bonit U=-25cm.; f=80a beyond Jens for mula =) t ==1/4 to tĚ = y20 to= to it's レニー4g = = 5-8 400 v=-400 =-133.33cm. Ass' near ponit 133-33cm for point Myppia resolved by Concave lenothe objeet placed at a should form its mage with inforpon't U=0; var fz-504 to te z7503 Uz-80cm. so far pornst 50 1050cm Ano and near pornit 133.33cm

Parallel rays from distant object (at infinity) Retina Image is Image) formed in front of the retina (a) In a myopic eye, image of distant object is formed in front of the retina (and not on the retina) -Retina 50cm Far point of Image is this eye formed on the retina (6) The far point (F) of a myopic eye is less than infinity Rays are first diverged by concave lens Parallel rays from distant Retina object (at ínfinity) F-- Image is Virtual formed on the retina image formed Concave lens to at F correct myopia (c) Correction of myopia. The concave lens placed in front of the eye forms a virtual image of distant object at far point (F) of the myopic eye o 50cm

25 cm Normal near point N Image formed behind the retina (a) More than 25 cm 133.33cm N' Near point of hypermetropic eye (b) -25 cm N' 123.33cm Convex lens converges the rays as if they are coming from n' (c)