Question

A transparent container contains layers of 3 immiscible transparent liquids of different refractive indices. A laser beam is pointed at the layer I as shown in the figure. 

 

What minimum angle of θ₁ will ensure that laser beam does not enter region III at all?

Answer 1

Snell’s law for each of the interfaces: 

\(n \sinθ_1 = n/3 . \sinθ_2 = n/5. sin(90)\) 

\(n \sinθ_1 = n/5. \sin(90) = n/5 \times 1\) 

\(\sinθ_1 = 1/5\) 

\(θ_1 = \sin^{-1} (1/5)\)