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The radius of curvature of the curved su...

The radius of curvature of the curved surface of a plano-convex lens is `20 cm`. If the refractive index of the material of the lens be `1.5`, it will

A

act as a convex lens only for the objects that lie on its curved side.

B

act as a concave lens for the object that lie on its curved side.

C

act as a convex lens irrespective of the side on which the object lies.

D

act as a concave lens irrespective of side on which the object lies.

Text Solution

Verified by Experts

The correct Answer is:
C
(i) If the object lies on the curved side, then `R_(1)=20cm` and `R_(2)=-oo`
Focal length is given by
`(1)/(f)=(mu-1)[(1)/(R_(1))-(1)/(R_(2))]`
`=(1.5-1)[(1)/(20)-((1)/(-oo))]=(1)/(40)`
`rArr" "f=40cm` (convex lens)
(ii) If the object lies on plane sie then
`R_(1)=oo and R_(2)=-20 cm`
Focal length is thus given by
`(1)/(f.)=(mu-1)((1)/(R_(1))-(1)/(R_(2)))`
`=(1.5-1)[(1)/(oo)-((1)/(-20))]=(1)/(40)`
`f=40cm" (convex lens)"`
The correct option is (c) .
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