Question

A person is advised to use 5D lens. What is its focal length?

• A. 50 cm
• B. 5 cm
• C. 2 cm
• D. 20 cm

Answer 1

The Correct Option is D

To solve the problem, we need to find the focal length of a lens when the lens power is given.

1. Understanding the Relationship Between Power and Focal Length:
The power of a lens ($P$) is related to its focal length ($f$) by the formula:

$ P = \frac{1}{f} $

where $P$ is the power in diopters (D) and $f$ is the focal length in meters.

2. Given Information:
The power of the lens is given as 5D, so:

$ P = 5 \, \text{D} $

3. Finding the Focal Length:
Using the formula $ P = \frac{1}{f} $, we can rearrange it to find $f$:

$ f = \frac{1}{P} = \frac{1}{5} $ meters

$ f = 0.2 \, \text{m} = 20 \, \text{cm}$

Final Answer:
The focal length of the lens is $ {20 \, \text{cm}} $