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## Homework Statement

A Capillary tube is made of glass of refractive index n

_{1}. The outer radius of the tube is R.The tube is filled with a liquid of refractive index n

_{2}< n

_{1}.what should be the minimum internal radius of the tube so that any ray that hits the tube would enter the liquid

## Homework Equations

## The Attempt at a Solution

I know that in an optical fibre they are core and cladding.it operates by principle of total internal reflection.i have calculated maximum incident angle possible

As i = arcsin √n

_{1}

^{2}

-n

_{2}

^{2}

How to get terms in terms of R and should we consider any size approximations as it is a capillary tube is what I can't understand.

If we should consider approximations then how?Please help me