Question

1. The nearest distance of distinct vision of

a hypermetropial person is 60 cm. If this
distance is reduced by 20 cm by using
spectacles. What is the nature and focal
length of the lens?
a. +30 cm b. +35 cm
-30 cm
d. -40 cm
c.​

Answer 1

The focal length of the lens is +30 and it is a convex lens.

Step-by-step explanation:

Given that,

The nearest distance of distinct vision of a hypermetropial person is 60 cm, v = -60 cm

The distance is reduced by 20 cm, u = -20 cm

We need to find the nature and focal length of the lens.

Let f be the focal length of the lens. Using lens formula,

`(1)/(v)-(1)/(u)=(1)/(f)\\\\(1)/(f)=(1)/((-60))-(1)/((-20))\\\\f=+30\ cm`

So, the focal length of the lens is +30 and it is a convex lens.