(a) What is meant by 'a beam of polarised light? (b) With the aid of well labelled diagrams, illustrate the action in of a polaroid spectacle on a beam of s...

(a) A beam of polarised light is light in which the vibrations are restricted to one direction or one plane only, perpendicular to the direction in which the light travels.

(b) As illustrated in the diagram above, sunlight is normally unpolarised. Its vibrations occur in many different planes perpendicular to the direction of travel.

When the sunlight falls on a horizontal surface such as a road, water surface or glass, the reflected light is largely polarised in a particular plane. This reflected polarised light produces glare.

A polaroid spectacle has a polaroid filter whose transmission axis is arranged vertically. The filter allows only the vertical component of the light vibrations to pass through it and absorbs the horizontal component, which is mainly responsible for glare reflected from horizontal surfaces.

• Unpolarised sunlight enters the spectacle lens.
• The polaroid lens acts as an analyser.
• Only vibrations parallel to the transmission axis of the lens emerge.
• The horizontally polarised reflected glare is greatly reduced or stopped.
• The wearer therefore sees more clearly and comfortably, especially when driving or viewing water.

Thus, polaroid spectacles reduce glare by selectively transmitting light vibrating in one plane only.