Light from a sodium lamp (S) passes through two polaroid sheets `P_(1)` and `P_(2)` as shown in figure. What will be the effect on the intensity of the light transmitted (i) by `P_(1)` and (ii) by `P_(2)` on rotating polaroid `P_(1)` about the direction of propagation of light ? Justify your answer in both cases.

Explanation

(i) When monochromatic light of Intensity lo passes through the polaroid Pi, the transmitted light becomes plane polarised whose intensity is `I_(1)= (I_(0))/(2)` . This intensity `I_(1)` does not change even on becomes plane polarised whose internsity is `I_(1)=(I_(0))/(2)` . This internsity `I_(1)` does not change even on rotating `P_(1)` about the direction of propagation of light.
(ii) If pass axis of polaroid sheet `P_(2)` subtends an angle `theta` with that of polaroid `P_(1)`, then in accordance with Malus law the intensity of transmitted light is `I_(2)=I_(1)cos^(2) theta=(1)/(2) I_(0)cos^(2) theta.` If polaroid sheet `P_(1)` is rotatecd about the direction of propagation of light, then value of 0 and consequently intensity `I_(2)` varies between the limiting values `(I_(0))/(2)` and zero.