Question

Your aunt just turned 50 and now needs glasses to read.

(a) What is the name of this condition? ("–opia")
(b) Does your aunt need converging lenses or diverging lenses?
(c) Your aunt goes to the store and buys glasses which say +0.75 (meaning, +0.75 D). What is the focal length of these glasses?
(d) Assuming these glasses (from part c) bring your aunt’s near point to 25 cm, what is her near point without corrective lenses?

Answer 1

(a) hypermetropia

(b) convex lens

(c) 133.33 cm

(d) - 21.05 cm

Step-by-step explanation:

(a) As she is old age, so she is suffering from hypermetropia.

(b) It is the defect due to which a person is not able to see the nearby objects clearly, so it is cured by convex lens of suitable focal length.

(c) Power, P = + 0.75 D

Focal length is the reciprocal of power of lens.

f = 1/ P = 1/0.75

f = 133.33 cm

(d) v = -25 cm, f = 133.3 cm

use lens equation

`(1)/(f)=(1)/(v)-(1)/(u)`

`(1)/(133.3)=(-1)/(25)-(1)/(u)`

`(-1)/(u)=(133.33+25)/(133.33*25)`

u = - 21.05 cm