Question

A person uses lens of power +2D name the defect of vision he is suffering from list two causes of the defect draw diagrams to show the formation in this case by the defective eye and correction made by the lens two thinning converging lenses of focal length 15cm and 30cm are held in contact calculate the power and the focal length of the combination

Answer 1

Person is suffering from Hypermetropia.
(CAUSES)
1) EITHER focal length of eye lens is too long, or
2) Shortening of eyeball due to some genetic defect.
(Diagram)
For defective eye - NCERT book - page - 190. fig(a)
For correction - fig. (c)

Converging lens are convex lens as they converge the rays.
focal length f = 15cm = 0.15m
power p = 1/f = 1/0.15 = 6.6D
focal length of another f' = 30cm = 0.3m
power p' = 1/f' = 1/0.3 = 3.3D
Power after combination = 6.6 + 3.3 = 9.9D