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Question
Find the focal length of a lens of power −2.0 D. What type of lens is this?
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Solution
Power of lens,
P = −2.0 D
P = `1/"f"`
∴ f = `1/"P"`
= `1/(-2.0 "D")`
= −0.5 m
A concave lens has a negative focal length. Hence, it is a concave lens.
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