- #1

arpon

- 235

- 16

## Homework Statement

Light falls on the surface AB of a rectangular slab from air. Determine the smallest refractive index n that the material of the slab can have so that all incident light emerges from the opposite face CD.

## Homework Equations

## The Attempt at a Solution

Let's think about this case:

There must be total internal reflection at Q and S.

That means, ##90-r>\theta _c## [##\theta _c## is the critical angle]

## sin(90-r)>sin \theta _c##

##cos r > \frac{1}{n}## [## sin \theta _c = \frac {1}{n}##]

##n>sec(r)##

But, the maximum value of ##sec(r)## is infinite.

That means n should be infinite.

But that is not the answer.