Question

The power of a convex lens of focal length \( 20 \text{ cm} \) is ....................

• A. \( +5.0 \text{ D} \)
• B. \( 0.20 \text{ D} \)
• C. \( -5.0 \text{ D} \)
• D. \( 0.5 \text{ D} \)

Hint:

To calculate the power of a lens, use the formula \( P = \frac{1}{f} \), where \( f \) is the focal length in meters. A positive power indicates a convex lens.

Answer 1

The Correct Option is A

The power \( P \) of a lens is given by the formula: \[ P = \frac{1}{f} \] where \( f \) is the focal length in meters. For a convex lens with a focal length of \( 20 \text{ cm} \) (or \( 0.2 \text{ m} \)): \[ P = \frac{1}{0.2} = 5.0 \text{ D}. \] The positive sign indicates it is a converging lens (convex lens).