1.

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` (Convex )C. `10 cm`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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