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Multiple Polarisers

  1. Sep 26, 2015 #1
    1. The problem statement, all variables and given/known data
    You use a sequence of ideal polarising filters, each with its axis making the same angle with the axis of the previous filter, to rotate the plane of polarisation of a polarised light beam by a total of 45°. You wish to have an intensity reduction no larger than 10%.

    What is the angle between multiple polarisers?

    2. Relevant equations

    3. The attempt at a solution
    For multiple polarisers I=Imaxcos2*n(θ/n) where n is an integer

    So I=cos2*n(θ/n) with I>0.9

    The only integer solutions I was able to obtain was 9 polarisers separated by 5 degrees (n=9). This would give I=0.933 which is less than 10% loss if Imax=1.

    However, this doesn't appear to be giving me the correct solution. What am I missing?
  2. jcsd
  3. Sep 26, 2015 #2


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    Using the formula, I find that n = 9 is not the smallest integer value of n that will work. (θ does not need to be an integer number of degrees.)
  4. Sep 27, 2015 #3
    Was using radians in solution. Thanks for making me look back and double-check!
  5. Sep 27, 2015 #4


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    OK. Good.
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