Question

A person needs a lens of power $+2\text{D}$ for correcting their near-sightedness. What is the focal length of the lens required to correct the defect?

• A. $2\text{m}$
• B. $0.5\text{cm}$
• C. $20\text{cm}$
• D. $50\text{cm}$

Answer 1

The correct option is D $50\text{cm}$

The power of a lens is the inverse of the focal length of the lens.

$⟹\text{P}=\frac{1}{f}$

Given:
The power of the lens, $\text{P}=+2\text{D}$
$⟹f=\frac{1}{\text{P}}=\frac{1}{+2}=0.5\text{m}$
$⟹f=50\text{cm}$