We want to rotate the direction of polarization of a beam of polarized light through 90 degrees by sending the beam through one or more polarizing sheets. (a) What is the mini-mum number of sheets required? (b) What is the minimum number of sheets required if the transmitted intensity is to be more than 60% of the original intensity? (Answer: (a) 2 sheets. (b) 5 sheets. )
(b) n=2, cos^4(90/2)=0.25
n=3, cos^6(90/3)=0.421875
n=4, cos^8(90/4)=0.530790
n=5, cos^10(90/5)=0.605429
So 5 sheets are required.
But how do I do part (a)?
(b) n=2, cos^4(90/2)=0.25
n=3, cos^6(90/3)=0.421875
n=4, cos^8(90/4)=0.530790
n=5, cos^10(90/5)=0.605429
So 5 sheets are required.
But how do I do part (a)?
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The answer to part (a) is 2 sheets, because if you used only 1 sheet with 90 degree polarisation, the transmitted intensity would be zero (=cos(90) ). Because the minimum intensity is > 0, two sheets is the minimum, each providing 45 degrees polarisation, giving 25% transmission as you've calculated in part (b).