Question

Unpolarized light of intensity ${I}_{0}$ is incident on the surface of a block of glass of Brewster’s angle. In that case, which one of the following statements is true?
A. Transmitted light is polarized with intensity $\dfrac {{I}_{0}}{2}$
B. Transmitted light is completely polarized with intensity less than $\dfrac {{I}_{0}}{2}$
C. Reflected light is partially polarized with intensity $\dfrac {{I}_{0}}{2}$
D. Reflected light is completely polarized with intensity less than $\dfrac {{I}_{0}}{2}$

Answer 1

Hint: When an unpolarized light is incident at Brewster’s angle, the light that is reflected from the surface of a block of glass, the light that is reflected from the surface is therefore perfectly polarized. A glass plate placed at Brewster’s angle in a light beam can be used as a polarizer. Thus, using the formula for Malus’s law, a solution to this question can be found.

Formula used: $I ={I}_{0} {\cos}^{2}{\theta}$
Where “I” is the intensity.

Complete step by step answer:
Malus’s law is given by,
$I ={I}_{0} {\cos}^{2}{\theta}$
Where, I is the intensity of transmitted light after polarization
            ${I}_{0}$ is the intensity of unpolarized light
When an unpolarized light is incident on a surface of a block of glass at Brewster’s angle then the transmitted ray is slightly polarized and the reflected light is completely polarized and the intensity of this reflected light is less than half the intensity of the incident light which is given as ${I}_{0}$. Thus, the intensity of reflected light is $\dfrac {{I}_{0}}{2}$.

So, the correct answer is “Option D”.

Note: If the $\theta= 0$ or 180°, then $I = {I}_{0}$. That is the intensity of transmitted light is maximum. Initial intensity and initial after polarization remain the same. If the $\theta= 90°$, then $I = 0$. That is the intensity of transmitted light is minimum. The intensity of light after polarization becomes zero. Brewster’s angle varies with the wavelength of the light.