Question

A beam of light strikes a piece of glass at an angle of incidence of 60 degree and the reflected beam is completely plane polarised.The refractive index of the glass is?

Answer 1

√3

Answer 2

• Concept: When unpolarized light is incident on a transparent medium at a specific angle (known as the polarizing angle or Brewster's angle, $\theta_B$), the reflected light is completely plane polarized. At this angle, the reflected ray and the refracted ray are perpendicular to each other.

• Brewster's Law: The refractive index ($\mu$) of the medium is related to the polarizing angle ($\theta_B$) by the formula: $\mu = \tan(\theta_B)$

• Given: The angle of incidence is 60 degrees, and the reflected beam is completely plane polarized. This implies that the angle of incidence is the polarizing angle. So, $\theta_B = 60^\circ$.

• Calculation: Substitute the value of $\theta_B$ into Brewster's Law: $\mu = \tan(60^\circ)$ $\mu = \sqrt{3}$

The refractive index of the glass is $\sqrt{3}$.