Question

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

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Solution

## 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, $P=\frac{1}{f}\phantom{\rule{0ex}{0ex}}Bysubstitutingthegivenvalue,weget\phantom{\rule{0ex}{0ex}}P=\frac{1}{-2}\phantom{\rule{0ex}{0ex}}=-0.5D$A concave lens of power of -0.5 D is required to fix the myopic eye.

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