Question

An unpolarized $He-Ne$ laser beam of wavelength $632.8\text{nm}$ is reflected from the flat surface of a dielectric. A detector analyzes the reflected beam. It is found that when the angle between the incident and the reflected beams is ${115}^{\circ }{34}^{{}^{\prime }}$ the light is completely plane polarized. The refractive index of the dielectric at this wavelength is

• A. 1.521
• B. 1.571
• C. 1.621
• D. 1.587

Answer 1

The correct option is D 1.587

$2i={115}^{\circ }-{34}^{{}^{\prime }}={115.566}^{\circ }$
$\therefore i=\frac{115.566}{2}={57.783}^{\circ }$
Refractive index $\left(\mu \right)=\tan i$ (By Brewster's law)
$=\tan \left({57.783}^{\circ }\right)=1.587$