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Homework Help: Unpolarized Light Intensity

  1. Sep 17, 2009 #1
    Unpolarized light from an incandescent lamp has an intensity 176 Cd as measured by a light meter. What is the intensity reading on the meter when two ideal are inserted between the bulb and the meter with their axis of polarization making an angle of θ = 40.0° relative to each other? Express your answer in Cd.

    am having some trouble with this problem. Here's what I have so far:

    Known info:

    Io=28 Cd

    Theta= 6o

    There are two polarizers, so theta1=6 and theta2=6


    I= Io/2

    Malus' Law: I= Iocos^2theta


    I used this to try and solve and it is wrong...

    I = 28/2



    I = 28(cos6)^2 which = 27.7 (at theta1)

    but there are two polarizers so 27.7 becomes the new Io for theta2

    I=27.7(cos6)^2 which =27.4

    So you add them right? 27.7+27.4 which = 55.1?

    Where am I getting confused?
  2. jcsd
  3. Sep 17, 2009 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Welcome to PF.

    For starters, the problem statement says 176 Cd and 40.0 degrees. Why are you using 28 Cd and 6 degrees when you work out the problem?
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