Question

1. The nearest distance of distinct vision of

Answer 1

Answer:

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

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,

$\dfrac{1}{v}-\dfrac{1}{u}=\dfrac{1}{f}\\\\\dfrac{1}{f}=\dfrac{1}{(-60)}-\dfrac{1}{(-20)}\\\\f=+30\ cm$

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