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Common Defects of the Eye

Lets say far ...

Question

Lets say far point of a myopic eye is 50 cm. It mean that he can only see till 50cm . So what should be the power of concave lens so that he can see object placed at infinite?

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Solution

Focal length= -farpoint
= -50 cm
p = power
p = 1/f ( f in metre)
p = 100/f (if f is in cm)
p=-100/50
p=-10/5
p=-2D Concave lens diverging lens
-ve sign indicates that it is concave lens.

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