A small coin is resting on the bottom of a beaker filled with liquid. A ray of light from the coin travels…

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?
  1. $2.4 \times 10^8 \mathrm{~m} / \mathrm{s}$
  2. $3.0 \times 10^8 \mathrm{~m} / \mathrm{s}$
  3. $1.2 \times 10^8 \mathrm{~m} / \mathrm{s}$
  4. $1.8 \times 10^8 \mathrm{~m} / \mathrm{s}$

Solution

$\because \quad \frac{1}{\mu}=\sin \theta_c=\frac{3}{5}$ $\begin{aligned} & \Rightarrow \quad \mu=\frac{5}{3} \\ & \text { And } v=\frac{c}{\mu}=\frac{3 \times 10^8}{5 / 3} \\ & =\frac{9}{5} \times 10^8=1.8 \times 10^8 \mathrm{~ms}^{-1} \end{aligned}$

Asked in: NEET 2007

Practice more Ray Optics questions on Aicharya