Polarizing windows, filters, etc. are often used to reduce the amount of light t
ID: 1451993 • Letter: P
Question
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 1310 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 25% of the original value?
Explanation / Answer
Here, average intensity after passing through first pane = 1310/2 = 655 W/m2
=> average intensity after passing through second pane = 327.5 W/m2
According to Malus Law
=> 327.5 W/m2 = 655 * cos2(theta)
=> cos2(theta) = 0.5
=> theta = 45 degrees --------------> angle should the polarizing axis of the second pane of the window make with the polarizing axis of the first pane of the window