A beam of light AO is incident on a glass slab (μ=1.54) in a direction as shown in figure. The reflected ray OB is passed through a Nicol prism, on viewing through the Nicole prism, we find on rotating the prism that

In the arrangement shown, the unpolarised light is incident at polarising angle of 90° – 33° = 57°. The reflected light is thus plane polarised light. When plane polarised light is passed through Nicol prism (a polariser or analyser), the intensity gradually reduces to zero and finally increases.