Q. The polaroid P1 , P2 & P3 are arranged coaxially. The angle between P1 and P2 is 37°. The angle between P2 and P3 is , if intensity of emerging light is one quarter of intensity of unpolarized light
(a) θ = cos-1 (5/4)
(b) θ = cos-1 (4/5)
(c) θ = cos-1 (4/(5√2))
(d) θ = cos-1 (5/(4√2))
Click to See Answer :
Ans: (d)
Sol: Let I0 = Intensity of unpolarised light
According to Malus’s Law
$\large I_2 = \frac{I_0}{2}cos^2 37^o $
$\large I_2 = \frac{I_0}{2}(4/5)^2 = \frac{8 I_0}{25}$
$\large I_3 = I_2cos^2\theta $
$\large \frac{I_0}{4} = \frac{8 I_0}{25}cos^2 \theta $
$\large cos^2 \theta = \frac{25}{32} $
$\large cos\theta = \frac{5}{4\sqrt{2}} $