Find the power and type of the lens by which a person can see clearly the distant objects, if a person cannot see objects beyond `40cm`A. `-2.5D` and concave lensB. `-2.5D` convex lensC. `-3.5D` and concave lensD. `-3.5D` and convex lens

Find the power and type of the lens by which a person can see clearly

1.	Find the power and type of the lens by which a person can see clearly the distant objects, if a person cannot see objects beyond `40cm`A. `-2.5D` and concave lensB. `-2.5D` convex lensC. `-3.5D` and concave lensD. `-3.5D` and convex lens
Answer» (a) Here, in this case the lens used by the person should form the image of distant object of `40cm` `:.u=oo,v=-40cm` and `1/f=1/v-1/u` `1/f=1/(-40)-1/(-oo)` `1/f=-1/40` Power `=1/f=-1/40=-2.5D` Negative sign shows that lens used is concave lens.

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Find the power and type of the lens by which a person can see clearly the distant objects, if a person cannot see objects beyond `40cm`A. `-2.5D` and concave lensB. `-2.5D` convex lensC. `-3.5D` and concave lensD. `-3.5D` and convex lens

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