Question

A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of what power?

Answer 1

Step (1) Given:

The far point of the person, $D=2m$

Step (2) Statement of Myopia:

Short-sightedness is an eye defect that causes the person to see far away objects as blurry or out of focus. The scientific term in use for short-sightedness is myopia.

From the given situation, the person is suffering from short-sightedness (or) myopia. A concave lens is used to correct myopia.

Step (3) Finding the focal length of the lens:

In the case of myopia, the focal length of the lens, $f=-D=-2m$

Step (3) Finding the power of the lens:

We know that the required power of the lens,

$$\begin{gathered} P=\frac{1}{f} \\ Bysubstitutingthegivenvalue,weget \\ P=\frac{1}{-2} \\ =-0.5D \end{gathered}$$

A concave lens of power of -0.5 D is required to fix the myopic eye.