The following five questions refer to the following situation. Originally, light

Question

The following five questions refer to the following situation. Originally, light is unpolarized. It then travels through 3 polarizers: the first with its transmission axis aligned vertical, the next at a 30 degree angle to the vertical and the last aligned at a 45 degree angle to the vertical (tilted the same direction as the first with respect to the vertical). The original intensity of light is 4 W/m2.

5)  What is the intensity of light after the third polarizer?

4 W/m2

2 W/m2

1.5 W/m2

1.4 W/m2

1.0 W/m2

0 W/m2

6)  If the second polarizer is aligned at a 45 degree angle to the vertical (just like the third), what is the final intensity of light after the third polarizer?

4 W/m2

2 W/m2

1.5 W/m2

1.4 W/m2

1.0 W/m2

0 W/m2

7)  If the second polarizer is aligned at a 45 degree angle to the vertical (but in the other direction), what is the final intensity of light after the third polarizer?

4 W/m2

2 W/m2

1.5 W/m2

1.4 W/m2

1.0 W/m2

0 W/m2

Explanation / Answer

Given,

I0 = 4 W/m^2

since, if it is unpolarized, I1 = I0/2

I1 = 4/2 = 2 W/m^2

I2 = I1 cos^2(30) = 2 x 0.866^2 = 1.5 W/m^2

I3 = I2 cos^2(45 - 30) = 1.5 x cos^2(15) = 1.4 W/m^2

Hence, I3 = 1.4 W/m^2 <<<<< ans(5)

6)I2 = I1 cos^(45) = 2 cos^45 = 1 W/m^2

Hence, I2 = 1 W/m^2 <<<< ans(6)

7)I2 = I1 cos^2(45 + 45) = 0

Hence, I2 = 0 W/m^2 <<<<< ans(7)

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