When light is incident on a transparent solid material, one

part of it gets reflected and another part gets refracted. If light is incident

on the interface between the two media such that there is 90° angle between the

reflected and refracted rays, the reflected light will be linearly polarized.

Brewster’s angle, or the

polarizing angle, is defined as an angle at which an incident beam of

unpolarized light is reflected after complete polarization.1

In this project

I will…. …

Background

In his studies on polarized light, Brewster discovered that when light

strikes a reflective surface at a certain angle, the light reflected from that

surface is plane-polarized. He elucidated a simple relationship between the

incident angle of the light beam and the refractive index of the reflecting

material. When the angle between the incident beam and the refracted beam

equals 90 degrees, the reflected light becomes polarized. This rule is often

used to determine the refractive index of materials that are opaque or

available only in small quantities.2

Brewster’s Angle and Polarized Light

When considering the incidence of non-polarized light on a flat

insulating surface, there is a unique angle at which the reflected light waves

are all polarized into a single plane. This angle is commonly referred to

as Brewster’s angle, and can be easily calculated utilizing the

following equation for a beam of light traveling through air:

n = sin (?i)/sin

(?r) = sin (?i)/sin (?90-i) = tan (?i)

Where n is the refractive index of the medium from

which the light is reflected, ?i is the angle of

incidence, and ?r is the angle of refraction. By

examining the equation, it becomes obvious that the refractive index of an

unknown specimen can be determined by the Brewster angle. This feature is

particularly useful in the case of opaque materials that have high absorption

coefficients for transmitted light, rendering the usual Snell’s law formula

inapplicable. Determining the amount of polarization

through reflection techniques also eases the search for the polarizing axis of

a sheet of polarizing film that is not marked.

For water (refractive index of 1.333) and glass (refractive index of

1.515 the critical (Brewster’s) angles are 53 and 57, degrees, respectively.

Hypothesis/Theory:

“When a beam of unpolarized light reflects

from a surface at the Brewster angle, the reflected beam will be polarized

along a direction parallel to the surface. The Brewster angle is the angle of

incidence that results in a 90° angle between the reflected and refracted

beams.”3

It is hypothesised that as the refractive index changes it will affect

Brewster’s angle.

Design and Methodology:

Equipment;

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Laser wavelength: 630-680 nm, power: