Explain the following giving reason for each:
(a) How does a polaroid work to produce a linearly polarised light from an unpolarised beam of light ?
(b) Why is it that light waves can be polarised but sound waves cannot be ?
(c) Why are sun goggles made of polaroids preferred over those using coloured glasses ?

Explanation

(a) A polaroid consists of long chain molecules aligned in a particular direction. Iff an unpolarised light is incident on such a polaroid, electric vectors of light waves along the direction of the aligned molecules get absorbed. Thus, in the emergent light there are electric vectors oscillating along a direction perpendicular to the aligned molecules and the light is therefore linearly polarised.
(b) Sound waves cannot be polarised because sound waves are longitudinal waves and longitudinal waves cannot undergo polarisation. light waves being transverse waves can be polarised.
(c) Sun goggles made of polaroids are preffered. when ordinary sunlight is incident on sun goggles, the transmitted light is plane polarised and its intensity is redused by half. sun goggles made of coloured glasses allow total light of a particular colour to pass.