Question

Three circularly shaped linear polarisers are placed coaxially. The transmission axis of the first polariser is at ${30}^o$, the second one is at ${60}^o$ and the third at ${90}^o$ to the vertical all in the clockwise sense. Each polariser additionally absorbs $10\%$ of the light. If a vertically polarised beam of light of intensity $I=100W/m^2$ is incident on this assembly of polarisers, then the final intensity of the transmitted light will be close to:

• A. $10W/m^2$
• B. $20W/m^2$
• C. $30W/m^2$
• D. $50W/m^2$

Answer 1

The correct option is C $30W/m^2$

$I_1=I_o\times 0.9co{s}^2{30}^o=I_o\times \frac{3}{4}$

$I_2=I_1\times 0.9co{s}^2{30}^o=I_1\times \frac{3}{4}$

$I_3=I_2\times 0.9co{s}^2{30}^o=I_2\times \frac{3}{4}$

$\therefore I_3=I_o\left(0.9{)}^3\right(\frac{3}{4}{)}^3$

$I_3=30.75\frac{W}{m^2}$