Question

A far-sighted man who has lost his spectacles, reads a book by looking through a small hole $(3 - 4mm)$ in a sheet of paper. The reason will be
A. Because the hole produces an image of the letters at a longer distance
B. Because in doing so, the focal length of the eye lens is effectively increased
C. Because in doing so, the focal length of the eye lens is effectively decreased
D. None of these

Answer 1

Hint:In case of a problem based on refraction of light through lenses, we know that defects in sight can be corrected using various types of lenses hence, remember the properties of the lens and analyze every option with the scientific approach, and check which option seems to be more appropriate for the given situation. Then, present the answer with a proper explanation.

Complete step by step solution:
According to the question, a man is suffering from far-sightedness which means ‘hypermetropia’. In this case of sight defect, the contact lens used is convex or converging in nature to correct this condition.

As we all know, the convex lens lowers the focal length of the light rays coming, and this results in a reduction of the distance of the image formed. Thus, A man who has lost his spectacles, when reading a book by looking through a small hole in a sheet was able to see the book ‘because in doing so, the focal length of the eye lens is effectively decreased’.

Hence, the correct option is C because in doing so, the focal length of the eye lens is effectively decreased.

Note: Since this is a problem of multiple-choice questions (theory-based) hence, it is essential that given conditions be analyzed very carefully to give a precise explanation. While writing an explanation of this kind of conceptual problem, always keep in mind to provide the exact reasons in support of your explanation.