Please Help Polarizing windows, filters, etc. are often used to reduce the amoun
ID: 1323400 • Letter: P
Question
Please Help
Polarizing windows, filters, etc. are often used to reduce the amount of light that enters the lens of a camera or into a room or a car. A library atrium has an overhead skylight that lets in too much light during the day, which heats up the interior of the library far too much. The building engineer installs new double-paned polarizing sky lights to reduce the intensity. If sunlight, which is unpolarized, has an average intensity of 1260 W/m2, what angle should the polarizing axis of the second pane of the window make with the polarizing axis of the first pane of the window in order to reduce the intensity of the sunlight to 40% of the original value?
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Explanation / Answer
from malus law
for first pane
I1 = Io/2
for second pane
I2 = I1*cos^theta
I2 = (Io/2)*(cos(theta))^2
give I2 = 31 % of Io
I2 = 0.31Io
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0.31*Io = (Io/2)*(cos(theta))^2
0.31 = 0.5*(cos(theta))^2
costheta = sqrt(0.31/0.5) = 0.787
theta = cos^-1(0.787)
theta = 38.1 degrees <----answer