Question

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A concave lens of refractive index 1.5 is immersed in a medium of refractive index 1.66. What is the nature of the lens ?

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Answer 1

Concave lens is immersed in medium having refractive index greater than the refractive index of the material of the lens therefore it will be have such converging lens .

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Answer 2

If refractive index of medium is greater then refractive index of lens then lens gain opposite nature .

E.g: When lens is initially cancave then after submerge in medium lens show convex nature and vice-versa .

reason :-

we know ,

1/v. - 1/u. = (d - 1){ 1/ R 1 - 1/ R 2}

d is the relative refractive index of system.

if initially (d -1){ 1/R 1 - 1/R 2} is positive

after submerge ,

d=1.5/1.65 <1 so, ( d-1 ) < 0

it means

(d - 1){ 1/R 1 - 1/R 2 } will be negative .

so,

answer of this question ,

lens will be convex .