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A thin equi-convex lens is made of glass...

A thin equi-convex lens is made of glass of refractive index `1.5` and its length is `0.2 m.` If it acts as a concave lens of `0.5 m` focal length when dipped in a liquid, the refractive index of the liquid is

A

`17//8`

B

`15//8`

C

`13//8`

D

`9//8`

Text Solution

Verified by Experts

The correct Answer is:
B
`(f_(1))/(f_(a)) = (n_(ga) - 1)/( n_(gl) - 1) rArr (-0.5)/(0.2) = (1.5 - 1)/(n_(gl) - 1)`
`rArr n_(gl) = 0.8 = (4)/(5)`
`rArr (n_(ga))/(n_(la)) = (4)/(5) rArr (1.5)/(n_(la)) = (4)/(5)`
`rArr n_(la) = (15)/(8)` .
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