Dolly and Ritu are two friends studying together in `V` grade. They prefer to sit together. Dolly is uncomfortable in reading the blackboard when they are sitting on the last bench. Dolly is depressed fearing that they may turn blind one day. Ritu explains to her that the problem may be due to some minor eye defect and there is no cause for worry. Dolly accompanied by Ritu visits the doctor who prescribes specs of suitable power for her. Dolly is now all smiles and thanks Ritu.
Read the above passage and answer the following questions :
(i) Name the eye defect Dolly is suffering from.
(ii) What could be the cause of this defect ?
(iii) The far point of Dolly is `50 cm`. What is the power of the lens she should use to read from the blackboard ?
(iv) What values are displayed by Ritu ?

Explanation

(i) Dolly is suffering from myopia or short sightedness.
(ii) Two possible cause of this defect are :
Increase in size of eye ball or decrease in focal length of eye lens.
(iii) Here,`x = 50 cm`
`f =-50 cm`
`P = (100)/(f) = (100)/(-50)= -2 D`
(iv) Ritu has displayed concern for her friend. She has explained to her that there is no cause for worry and Dolly can be treated for her problem. And the doctor has provided Ritu right.