Question

A small coin is resting on the bottom of a beaker filled with a liquid. A ray of light from the coin travels upto the surface of the liquid and moves along its surface (see figure).

How fast is the light travelling in the liquid?

• A. $1.2\times 10^{8}ms^{- 1}$
• B. $1.8\times 10^{8}ms^{- 1}$
• C. $2.4\times 10^{8}ms^{- 1}$
• D. $3.0\times 10^{8}ms^{- 1}$

Answer 1

Answer: (B)

$sin\theta _{C}=\frac{\mu _{R}}{\mu _{D}}=\frac{v_{D}}{v_{R}}$
$\frac{6}{10}=\frac{v_{D}}{3 \times 10^{8}}$
$v_{D}=1.8\times 10^{8}ms^{- 1}$