When light falls on two polaroid sheets, one observes complex brightness then the two polaroids axes are

When light falls on two polaroid sheets, one observes complete brightness then the two polaroids axes are

When light falls on two polaroid sheets having their axies matually perpendicular, then it is

Write two uses of polaroids?

Light from an ordianry source(say a sodium lamp) is passed through a polaroid sheet P_1 .The transmitted light is then made to pass through a second polaroid sheet P_2 ,which can be rotated so that the angle (theta) betwen the two polaroid sheets varies from 0^@ to 90^@ .Show graphically the variation of he intensity of light transmitted by P_1 and P_2 as a function of the angle theta .Take the incident beam intensity as I_0 . Why does the light from a cleear blue portion of the sky,show a rise and fall on intesnity,when viewed through a polaroid ,which is rotated?