Question

A person needs a lens of power + 3D for correcting his near vision and -3D for correcting his distant vision. Calculate the focal lengths of the lenses required to correct these defects.

Answer 1

Answer:

focal length of one lens is 0.333m

focal length of another lens is -0.333m

Answer 2

The focal lengths of the lenses required to correct these defects are 33.3 cm and -33.3 cm respectively.

Explanation:

Given that,

Power of the lens for correcting near vision, P = +3 D

Power of the lens for correcting distant vision, P' = -3 D

We need to find the focal lengths of the lenses required to correct these defects. We know that the reciprocal of focal length is called the power of a lens.

Focal length of the lens used to correct near vision

$f=\dfrac{1}{P}\\\\f=\dfrac{1}{3}\\\\f=0.333\ m\\\\f=33.3\ cm$

Focal length of the lens used to correct distant vision

$f'=\dfrac{1}{P'}\\\\f'=\dfrac{1}{-3}\\\\f'=-0.333\ m\\\\f'=-33.3\ cm$

So, the focal lengths of the lenses required to correct these defects are 33.3 cm and -33.3 cm respectively.

Learn more,

Power of a lens

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