Polarizers 1 and 3 have their axes of polarization, indicated by the black solid

Question

Polarizers 1 and 3 have their axes of polarization, indicated by the black solid lines, perpendicular to each other. If you try to shine light through only the combination of 1 and 3, you will find that none passes through. However, now we put in another polarizer (number 2 in the figure) between number 1 and number 3. This polarizer has an axes of polarization that has an angle of ? = 25° with respect to the polarization axes of polarizer 1. Surprisingly, now some light passes through the combination 1+2+3. What percentage of the initial (unpolarized) light intensity passes through?

Explanation / Answer

malus law = I = Io*cos^(theta)

I1 = Io/2

I2 = I1*cos^2(25)

I2 = 0.82 I1 = 0.41 Io

I3 = I2 * cos^(theta)

theta =90 -25 = 65 degree

I3 = I2 *cos^(65)

I3 = 0.1786 I2 = 0.1786 * 0.41 Io

I3 = 0.073226 Io = 7.3226 % of Io

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