Question

For a person near point of vision is 100cm. what should be the power, nature of lens he must wear so as to have normal vision?Draw the ray diagram.

Answer 1

we know that power = 1/focal length so we have to find the focal length first.

Given that image distance (v) = 100cm = -100cm = -1m .Since object distance (u) is not given it is to be considered as infinity that is 0.

Now we know that 1/v - 1/u = 1/f

1/-100 - 1/0 = 1/f

-1/100 - 0 =1/f

-1/100 = 1/f

f = -100cm

now to find power of lens we use the formula power = 1/f(in meters)Dioptres

=1/-100(cm)

=1/-1(in m)

=-1D

since power is negative so the person must wear a concave lens. Which means that he is suffering from myopia.