The picture given here shows a person wearing 'half-moon' spectacles. What sort of eye-defect do you think he has ? Why are these particular spectacles useful to him?

A person finds difficulty in seeing nearby objects clearly. His vision can be corrected by using spectacles containing :

In a certain murder investigation, it was important to discover whether the victim was long-sighted or short-sighted. How could a detective decide by examining his spectacles?

A short-sighted person has a near point of 15 cm and a far point of 40 cm.

(a) Can he see clearly an object at a distance of:

(i) 5 cm ? (ii) 25 cm ? (iii) 50 cm ?

(b) To see dearly an object at infinity, what kind of spectacle lenses does he need ?

The near point of a long-sighted person is 50 cm from the eye.

(a) Can she see dearly an object at:

(i) a distance of 20 cm ? (ii) at infinity ?

(b) To read a book held at a distance of 25 cm, will she need converging or diverging spectacle lenses?