Question

What is meant by polarization of light? Describe a method to obtain plane polarized light by reflection.

Hint:

To remember the orientation of polarization by reflection, think of the electric field vibrations as arrows. The vibrations parallel to the surface are more likely to be transmitted/refracted, while those perpendicular to the plane of incidence are more easily reflected. This is why sunglasses with Polaroid filters are effective at reducing glare from horizontal surfaces like water or roads.

Answer 1

Meaning of Polarization of Light:
Light is a transverse electromagnetic wave, which means the oscillations of its electric field vector occur in a plane perpendicular to the direction of wave propagation. Ordinary (unpolarized) light consists of waves with electric field vectors vibrating in all possible directions in this plane. Polarization is the phenomenon of restricting these vibrations of the electric field vector to a single direction (or plane). The resulting light is called plane-polarized or linearly polarized light.
Method to Obtain Plane Polarized Light by Reflection:
Plane polarized light can be obtained from unpolarized light using the phenomenon of reflection, based on a principle discovered by David Brewster.
Principle (Brewster's Law): When unpolarized light is incident on the boundary between two transparent media (e.g., air and glass), the reflected light becomes completely plane-polarized if the angle of incidence is equal to a specific angle called the polarizing angle or Brewster's angle (\(i_p\)).
Description of the Method: \begin{enumerate} \item An unpolarized light beam is directed towards a smooth, transparent surface, such as a glass slab. \item The angle of incidence (\(i\)) is adjusted by rotating the slab. \item At a specific angle of incidence, \(i = i_p\), it is observed that the reflected light is completely plane-polarized. The vibrations of the electric field vector in this reflected polarized light are perpendicular to the plane of incidence (the plane containing the incident ray, reflected ray, and the normal). \item At this polarizing angle, the reflected ray and the refracted ray are found to be perpendicular to each other. \item Brewster's Law gives the relationship between the polarizing angle and the refractive index (\(n\)) of the medium: \[ n = \tan(i_p) \] \end{enumerate} Therefore, by making unpolarized light incident on a transparent surface at Brewster's angle, we can obtain a completely plane-polarized reflected beam.