Question

A mans near point is .5 m and far point is 3m ...Power of spectacles required is

Answer 1

ANSWER:-

Persons near point,v = -50 cm

Least distance of distinct vision,u = -25 cm

By lens makers formula

1/f = 1/v - 1/u

Substituting and calculating we get

f = 50 cm

Power = 1/ f = 1/ 50cm

= 1/0.5 m

= 2 D (Convexlens)

To read a book kept at the least distance of distinct vision he should use a convex lens of power 2 D.

b) Persons far point is 3 m

i e. focal length,f = farpoint = -3 m

Power of lens = 1/f

= 1/-3

=-0.33 D (Concave lens)

To see birds flying at distance larger than 3 m he have to use a concave lens of power -0.33 D.