Question

A simple magnifying glass consists of _______________.
A) a concave lens
B) a convex lens of large focal length
C) a convex lens of small focal length
D) a plane mirror

Answer 1

Hint: An object is said to be magnified if the image produced has a size greater than the size of the object. The image produced by the magnifying glass will serve as the object for the eye. So the image produced by the magnifying glass must itself be large. A convex lens forms enlarged images.

Complete step by step answer:
Step 1: Mention the features of the convex lens.
A convex lens is a converging lens i.e., the light rays entering the lens will be converged at a point after refraction. When an object is placed between the focus and the optical center of a convex lens, the image formed will be virtual and upright. Also, the size of the image will be larger than the size of the object.
Step 2: Sketch the ray diagram for the image produced by a convex lens when the focal length is small and large.

From the above two figures, we see that the size of the image formed is larger for a convex lens of smaller focal length. Thus a convex lens of the small focal length is used as a magnifying glass.

$\therefore$ The correct option is C.

Note:
A plane mirror forms a virtual and erect image of the object but it will be of the same size as that of the object and hence it cannot be used as a magnifying glass. The image formed by a concave lens is virtual and upright but the image will be highly diminished. So a concave lens cannot be used for this purpose.