Question

Which of the following lenses would you prefer to use while reading the small letters found in dictionary.and why?


a. A convex lens of focal length 30 cm.

b. A concave lens of focal length 30 cm.

c. A concave lens of focal length 5 cm.

d. A convex lens of focal length 5 cm.

Answer 1

A convex lens gives a magnified image of an object when it is placed between the radius of curvature and focal length. Also, magnification is more for convex lenses having shorter focal length. Therefore, for reading small letters, a convex lens of focal length 5 cm should be used.

Answer 2

Hiii friends!

Image formed by a convex lens between 2F and the optic center is a magnified image.

To read small letters in the dictionary, we need to use a magnifying lens which is convex lens.

Answer : option D

Convex lens of focal length 5

Why focal length is 5cm ?

Reason:

When the focal length is smaller we obtain a magnified image .

When the focal is greater , we obtain diminished image.