Question

The focal length of the glasses of a shortsighted person is 40 cm. What is the nature of lens and its power?

Options

• Convex, 2.5 D

• Concave, −2.5 D

• Convex, 2.0 D

• Concave, −2.0 D

Answer 1

Concave, −2.5 D

Explanation:

Short-sightedness is corrected with a concave lens, which has negative focal length and power.

Using $$\text{P} = \dfrac{100}{f\text{ (in cm)}}$$

$$= \dfrac{100}{-40}$$

= −2.5 D