Question

A watch maker’s glass is a
(A) Convex lens.
(B) Concave lens.
(C) Plans- Convex lens.
(D) Plano- Concave lens.

Answer 1

Hint: Watch- maker’s glass is the lens used by the watchmaker to help him mechanize a watch. You should know that the distance between the eye of a watchmaker and his watch is very less.

Complete step by step answer:
There are some points by which we can easily understand the use of watch- maker’s glass and what is the use of it.
First we will understand what a convex lens is and where it is used.Convex lens is used in eyeglasses for those who have problems in identifying objects close to them. For example, problems in reading.It usually happens because the distance between the eye’s lens and retina reduces in the human eye. As a result of which the focal point lies behind the retina.
Eyeglass with convex lens increases refraction and accordingly reduces the focal length. This helps the person wearing glasses to form the image at the retina, helping him/her to be able to see closer objects clearly.The same concept is helpful for the watchmaker as when he uses the convex lens, the images he sees look larger than they are. Which helps him to be able to see the small gears in the watch clearly.Convex lenses show magnified images to the watchmaker. And he can choose the convex lens with required magnification according to his need.So, the small parts of a watch are clearly visible by the watchmaker by the help of the convex lens.This helps him repair and manufacture the small crucial parts of a watch.
So, the correct answer is option (A) Convex lens.

Note:Watch maker’s use glass to magnify the small parts of the watch. And we know that the magnifying lens is a convex lens. Thus the watch maker uses a convex lens.