What are polaroids ? Mention some of their practical uses ?

Explanation

Polaroids : Polaroids are thin and large sheets of crystalline polarising materials which polarises light. Tourmaline is a natural polarising materal. A synthetic crystalline materials quinine iodo-sulphate has the property of polarising the light. A large number of these crystals with their parallel to each other are packed in between two sheets of plastic which serves as the polaroid.
Uses of polaroids :
(i) Polaroids are widely used as polarising sunglasses.
(ii) Polaroids films are used to produce three dimensional moving pictures.
(iii) Polaroids are used to improve colour contact in old oil paintings.
(iv) Polaroids are used in optical stress analysis.
(v) Polaroids are used to eliminate the head light glare in motor cars.
(vi) Polaroids are used in glass window in trains and aeroplanes.