Question

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A converging lens of refractive index 1.5 is kept in a liquid medium having same refractive index. What would be the focal length of the lens in this medium?


Answer with Full explanation.​

Answer 1

$\huge\sf\blue{Question}$

A converging lens of refractive index 1.5 is kept in a liquid medium having same refractive index. What would be the focal length of the lens in this medium?

$\huge\sf\blue{Answer}$

Refractive index of the lens = 1.5 = Refractive index of the medium.

The lens in the liquid will act like a plane sheet of glass. 

∴ Its focal length will be infinite (∞) 

By using the formula of lens maker, 

$\frac{1}{f}=(u-1)[\frac{1}{R1}-\frac{1}{R2}]$

$\frac{1}{f}=\frac{u2}{u1}-1[\frac{1}{R1}-\frac{1}{R2}]$

u1=u2

$\frac{1}{f}=0$

Thus, $\sf\red{f=}$$\sf\red\infty$

Answer 2

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refer to the attachment

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