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,
[tex]\dfrac{1}{v}-\dfrac{1}{u}=\dfrac{1}{f}\\\\\dfrac{1}{f}=\dfrac{1}{(-60)}-\dfrac{1}{(-20)}\\\\f=+30\ cm[/tex]
So, the focal length of the lens is +30 and it is a convex lens.
