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A person who can see things most clearly at a distance of `10 cm`. Requires spectacles to enable to him to see clearly things at a distance of `30 cm.` What should be the focal length of the spectacles ?A. `15 cm` (Concave)B. `15 cm` (Concave)C. `10cm`D. `0` |
Answer» Correct Answer - A For lens `u=` wants to see `=-30cm` and `v=` can see`=-10cm` `:. (1)/(f)=(1)/(v)-(1)/(u)=(1)/(-10)-(1)/((-30))` `impliesf=-15cm` |
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