Question

A light ray refracted from air to a denser medium. The angle of incidence is 60° and the angle of refraction is 30°. If the speed of light in air is $3\times {10}^{8}m/s$, find the speed of light in the denser medium.

[2 marks]

• A. $2.5\times {10}^{8}m/s$
• B. $1.8\times {10}^{8}m/s$
• C. $1\times {10}^{8}m/s$
• D. $5.1\times {10}^{8}m/s$

Answer 1

The correct option is B $1.8\times {10}^{8}m/s$

Given,
Angle of incidence, i = 60°
Angle of refraction, r = 30°

Refractive index of the medium $=\frac{\sin i}{\sin r}$

$=\frac{\sin {60}^{\circ }}{\sin {30}^{\circ }}$

$=\sqrt{3}$

$=1.7$


Refractive index of the medium = $\frac{Speedoflightinair}{Speedoflightinmedium}$
$1.7=\frac{3\times {10}^{8}m/s}{Speedoflightinmedium}$

Speed of light in the medium
$=\frac{3\times {10}^{8}m/s}{1.7}$
$=1.8\times {10}^{8}m/s$