Question

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

• A. $2.4\times 10^{8}m/s$
• B. $1.8\times 10^{8}m/s$
• C. $3.0\times 10^{8}m/s$
• D. $5.0\times 10^{5}m/s$

Answer 1

Answer: (B)

From figure, $OA=4cm,AB=3cm$
$\therefore OB=\sqrt{4^2+3^2}=5cm$
Now, $\mu =\frac{1}{\sin C}=\frac{1}{AB/OB}=\frac{OB}{AB}=\frac{5}{3}$
From, $\mu =\frac{C}{C/v}=\frac{C}{\mu }=\frac{3\times 10^8}{5/3}$
$=1.8\times 10^{8}m/s$