Question

What is the focal length of a lens if its power is \( +2 \, \text{D} \)?

• A. 0.5 m
• B. 1.0 m
• C. 2.0 m
• D. 0.2 m

Hint:

Remember: The power of a lens is the reciprocal of its focal length. The unit of power is diopter (D), and the focal length is in meters.

Answer 1

The Correct Option is A

Step 1: Use the formula for the power of a lens The power \( P \) of a lens is related to its focal length \( f \) by the formula: \[ P = \frac{1}{f} \] where: - \( P \) is the power of the lens (in diopters), - \( f \) is the focal length of the lens (in meters). Step 2: Solve for \( f \) Given that the power of the lens is \( P = +2 \, \text{D} \), substitute this into the formula: \[ 2 = \frac{1}{f} \] Now, solve for \( f \): \[ f = \frac{1}{2} = 0.5 \, \text{m} \] Answer: Therefore, the focal length of the lens is 0.5 m. So, the correct answer is option (1).