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A plano-convex lens of radius of curvatu...

A plano-convex lens of radius of curvature 30 cm and refractive index 1.5 is kept in air. Find its focal length (in cm).

A

30

B

60

C

15

D

120

Text Solution

Verified by Experts

The correct Answer is:
B
From Lens maker.s formula,
In `1/f=(mu-1)[(1)/(R_1)-(1)/(R_2)],R_1=infty,R_2=-30` cm
`therefore 1/f=(1.5-1.0)[(1)/(infty)-(1)/(-30)]`
`therefore 1/f=0.5 xx(1)/(30)=(1)/(60)`
`therefore` f=60 cm
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