The expected answers are:

   (a)      In plane polarized light, the vibrations of the particles are confined to
             a single plane while in ordinary light, the particles vibrate in many
             planes                 

                               
     (b)            Polaroid
               e.g.      -    used in sun glasses to reduce the intensity of sunlight
                        -    used to eliminate reflected light or glare
                        -    sacharimetry/measurement of concentration of sugar solution
                        -    (photo elastic) stress analysis
                        -    production of three dimensional fil