Question

A person cant see the object beyond $25cm$ ,the power of lens to correct the vision will be

• A. $-4D$
• B. $-2D$
• C. $-1D$
• D. $2D$

Answer 1

The correct option is A

$-4D$

Step 1: Formula used

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

$f=$ focal length

$D$ is unit of power (diopter)

Step 2: Calculation

Given : $f=25cm=0.25m$

$$\begin{gathered} P=-\frac{1}{f}D \\ P=-\frac{1}{0.25}D \\ P=-4D \end{gathered}$$

Hence, option (a)$-4D$ is the correct answer.