Question

Unpolarised light of intensity 32 W m${}^{-2}$ passes through three polarizes is crossed with that of the first. The intensity of final emerging light is 3 W m${}^{-2}$. The intensity of light transmitted by first polarizer will be

• A. 32 W m${}^{-2}$
• B. 16 W m${}^{-2}$
• C. 8 W m${}^{-2}$
• D. 4 W m${}^{-2}$

Answer 1

The correct option is B 16 W m${}^{-2}$

Intensity of polarised light transmitted from 1st polariser,
$I_1$ = $I_0$ cos${}^2\theta$
but (cos${}^2\theta {)}_{av}=\frac{1}{2}$
So $I_1$ = $\frac{1}{2}{I}_0=\frac{32}{2}=16W{m}^{-2}$