At what angle should the axes of two Polaroids be placed so as to reduce the intensity of the incident unpolarized light to (a) (1/3), (b) (1/10)

35.3°

18.4°

Explanation:

a.

The first polariser polarises the unpolarised light reducing its intensity from I0 to I0/2. We have to reduce the intensity from I0/2 to I0/3.

Using to Law of Malus, I=I0cos²θ

cos²θ=I/I0=(I0/3)/I0/2 ,

cosθ=√2/3−−√=0.6667−−−−−√=0.8165

θ=cos−1(0.8165)=35.3∘

B.

Cos²θ=I/Io =Io/10/Io9

Cosθ= √9/10= 0.9487

= cos−10.9487

=18.4°

the correct choice is a .

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