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Polarisation by Reflection and Refraction

Edexcel AS-level PhysicsOpticsLesson 17 of 21

Polarising filters are not the only way to polarise light. When unpolarised light is reflected from a non-metallic surface, such as water, glass or a wet road, the reflected light is partially plane polarised. More of its oscillations are parallel to the reflecting surface, so light reflected from a horizontal surface is mostly polarised in the horizontal plane.

The light that is refracted into the material is also partially polarised, with more of its oscillations in the plane at right angles to those in the reflected light.

At one particular angle of incidence, called the Brewster angle, the reflected light is completely plane polarised. This happens when the reflected ray and the refracted ray are at 90° (perpendicular) to each other. For water the Brewster angle is about 53°.

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Key terms in this lesson

transmission axis
The direction within a polarising filter along which wave oscillations are transmitted; oscillations at right angles to it are absorbed.

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