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Saturday, April 24, 2010

As#9: Polarization of Light and Malus's Law (PART F)

The question reads:

Notice that a polarizer modifies the light intensity according to Malus's law and also reorients the polarization angle of the beam to match its own transmission axis. Hence it is possible for light to pass through a pair of crossed polarizers if a third polarizer is inserted between them with an intermediate transmission axis direction. What is the new intensity of the light emerging from the final polarizer in Part E if a third polarizer (Polarizer A in the figure (Part F figure) ), whose transmission axis is offset 45 from each of the others, is inserted between the original two polarizers?

I thought that becuase the first polarizer and the third polarizer are perpendicular to each other, they would form an intensity of zero regardless of whatever angle the second polarizer is positioned at in the misddle. I dont understand this.

Any help?


  1. Well, what I understand from reading the book is that as long as the angle between 2 adjacent polarizer is not 90 degrees, the light can be transmitted.
    Even if, let say the angle between 1st & 2nd polarizer is 20, between 2nd & 3rd is 30, between 3rd & 4th is 40. The total of angle is 90 (20+30+40), however, the final intensity is not zero.
    Also if we use the law of Malus for above condition, we'll see that the final intensity is 0.19 I(not)
    the only angle that can make the intensity zero is 90, because cos 90 is zero.
    Hope this helps :)

  2. Did that answer your question Kulsoom


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