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A concave or convex lens is given such t...

A concave or convex lens is given such that radii of curvature are same. If refractive index of glass is 1.5, then its focal length = ...... where R = radius of curvature.

A

R

B

`R/2`

C

2R

D

`1/4R`

Text Solution

Verified by Experts

The correct Answer is:
A
`1/f=(n-1)(1/R_1-1/R_2)`
`=(1.5-2)2/R=1/R` (convex)
`thereforef=R`
`1/f=(n-1)(-1/R-1/R)` (concave)
`=-(1.5-1)2/R=-1/R`
`therefore f=-R` `therefore`f=R(value)
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