Question

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

• A. A convex lens of focal length 50 cm.
• B. A concave lens of focal length 50 cm.
• C. A convex lens of focal length 5 cm.
• D. A concave lens of focal length 5 cm.

Answer 1

The correct option is C

A convex lens of focal length 5 cm.

Explanation for correct option: Option C: Convex lens:

1. When an object is placed at the focal point and between the pole and focus, a convex lens creates an enlarged and virtual image of it.
2. Convex lenses are also known as converging lenses because the rays that fall on the convex lens converge.
3. A convex lens acts as a magnifying glass when it forms a virtual, erect, and magnified image of an object. For this, the object is to be placed between the principal focus and the optical center of the lens.
4. The convex lens is used in the projector to get the magnified image.
5. A convex lens with a focal length of 50 cm is not preferred because convex lenses with higher focal lengths have lower magnification.
6. Thus, a convex lens of a focal length of 5 cm is preferable for reading small letters found in a dictionary.

An illustrative diagram of a convex lens is shown below.

Hence, option (C) is correct.