Q. Unpolarised light passes through a polariser and analyser which are at an angle of 45° with respect to each other. The intensity of polarised light coming from analyser is 5W/m². The intensity of unpolarised light incident on polariser is
(a) 5√3 W/m²
(b) 10 W/m²
(c) 20 W/m²
(d) 5 √3/4 W/m²
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Ans: (c)
Sol: According to Malus Law
I2 = I1cos2 θ
I2 = I1cos2 45°
$ \displaystyle I_2 = \frac{I_0}{2}cos^2 45 $
$\displaystyle 5 = \frac{I_0}{2}\times \frac{1}{2} $
I0 = 20 W/m2