Question

A child while playing with his fathers spectacles burnt a hole in a piece of paper by focussing a small image of sun on it. what is his fathers eye defect

Answer 1

Convex lens is also called as converging lens as it can converge the refracted rays at one point on principal axis called Focus .
It's clear that child used spectacles having convex lens to burn paper as it focussed Sunrays at a point.
Conclusion:
Child's father is suffer with hypermetropia where he can see far things clearly and finds difficulty in seeing near things
Corrective measures used for eyedefect: Doctor suggest convex lens spectacles.

Answer 2

It was convex lens in spectacles which focuses scattered sun rays at one point which can burn a piece of paper and dry leaves etc. Convex lens are used in near vision eye defect in which a person can clearly see far things but finds it difficult to see near things.