Q: A beam of unpolarized light of intensity I0 is passed through a polaroid A and then through another polaroid B which is oriented so that it principal plane makes an angle of 45° relative to that of A . The intensity of emergent light is
(a) I0
(b) I0/2
(c) I0/4
(d) I0/8
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Ans: (c)
Sol: Here, polaroid A polarizes light.
Intensity of polarized light from A= I0/2
According to law of Malus ,
Intensity of light emerging from B,
$\displaystyle I_B = \frac{I_0}{2}cos^2 45^o $
$\displaystyle I_B = \frac{I_0}{2}(\frac{1}{\sqrt{2}})^2 $
$\displaystyle I_B = \frac{I_0}{4} $