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

I_{2} = I_{1}cos^{2} θ

I_{2} = I_{1}cos^{2} 45°

$ \displaystyle I_2 = \frac{I_0}{2}cos^2 45 $

$\displaystyle 5 = \frac{I_0}{2}\times \frac{1}{2} $

I_{0} = 20 W/m^{2}