Question

A small coin is resting on the bottom of a beaker filled with liquid. A ray of light from the coin travels upto the surface of the liquid and moves along its surface.
How fast is the light travelling in the liquid?

• A. $ 2.4 \times {10}^8 m/s$
• B. $ 3.0 \times {10}^8 m/s$
• C. $ 1.2\times {10}^8 m/s$
• D. $ 1.8 \times {10}^8 m/s$

Answer 1

Answer: (D)

$ \frac{1}{\mu}=\sin \theta_{C} =\frac{3}{5}$
$ \Rightarrow \mu=\frac{5}{3} $
$\Rightarrow v =\frac{ c }{\mu} =\frac{3 \times 10^{8}}{5 / 3}=\frac{9}{5} \times 10^{8} $
$=1.8 \times 10^{8}\, ms ^{-1} $