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(C) Let $I_0 = 32 \ W m^{-2}$ be the intensity of unpolarised light.After passing through the first polaroid,the intensity becomes $I_1 = I_0 / 2 = 32

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$30$

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(C) Let $I_0 = 32 \ W m^{-2}$ be the intensity of unpolarised light.After passing through the first polaroid,the intensity becomes $I_1 = I_0 / 2 = 32 / 2 = 16 \ W m^{-2}$.Let $	heta$ be the angle between the axes of the first and second polaroid. The intensity after the second polaroid is $I_2 = I_1 \cos^2 	heta = 16 \cos^2 	heta$.The angle between the second and third polaroid is $(90^{\circ} - 	heta)$ because the first and third are crossed.The intensity after the third polaroid is $I_3 = I_2 \cos^2(90^{\circ} - 	heta) = I_2 \sin^2 	heta$.Substituting $I_2$,we get $I_3 = 16 \cos^2 	heta \sin^2 	heta = 16 (\sin 	heta \cos 	heta)^2 = 16 (\sin(2	heta) / 2)^2 = 4 \sin^2(2	heta)$.Given $I_3 = 3 \ W m^{-2}$,we have $4 \sin^2(2	heta) = 3$,so $\sin^2(2	heta) = 3/4$.Thus,$\sin(2	heta) = \sqrt{3}/2$,which implies $2	heta = 60^{\circ}$ or $120^{\circ}$.Therefore,$	heta = 30^{\circ}$ or $60^{\circ}$.

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