Question

A glass lens of refractive index 145 disappears when immersed in a liquid. What is the value of
refractive index of the liquid.
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Answer 1

Answer:

Refractive index means ratio of speed of light in vacuum and speed of light in any medium. here glass lens will be disappears when we immersed the lens into a liquid . It means speed of light through lens for air medium is same as speed of light through lens for liquid medium. e.g., refractive index of lens with respect to medium = 1 . or you can say that refractive index of lens = refractive index of liquid .

That's why refractive index of liquid = 1.45

In another way,

as you know, formula for focal length of any lens

here, μ is refractive index of lens with respect to medium

e.g.,

when lens is disappears means power of lens goes to zero.

so, P = 1/f = 0 , f = ∞

it means μ = 1 [ here , we assume ( 1/R₁ - 1/R₂) ≠ 0 ]

hence, refractive index of lens = refractive index of medium = 1.45