Question

A girl use lens of focal length -50cm. name the defect of vision, she is suffering from. What is the power of lens?

Answer 1

Answer:

Explanation:

She is using concave lens i.e she is suffering from myopia

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Answer 2

we have focal length as a negative value

key point: focal length of convex lens is always positive while focal length of concave lens is always negative.

therefore she is using a concave lens, which means she have the disease myopia or shortsightedness.

Power of lens = 1/focal length in metres.

therefore, $P= \frac{1}{f in m}$ $= \frac{1}{-0.5m} = -2Dioptre$

so power = -2D

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