What are the two most common defects of vision (or defects of eye)? How are they corrected?

A student sitting in the last row of the class-room is not able to read clearly the writing on the blackboard.

(a) Name the type of defect he is suffering from.

(b) How can this defect by corrected?

Complete the following sentences:

(a) A short-sighted person cannot see _______ objects clearly. Short-sightedness can be corrected by using

_______ lenses.

(b) A long-sighted person cannot see _______ objects clearly. Long-sightedness can be corrected by using

_______ lenses.

Differentiate between myopia and hypermetropia. What type of spectacles should be worn by a person having the defects of myopia as well as hypermetropia? How does it help ?

Name the defect of vision which can be corrected by a converging lens. Show clearly by a ray diagram how the lens corrects the defect.