Question

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 minimum number of sheets required (assuming the power of the passing-through beam can be as small as possible, but not zero).

(b) What is the minimum number of sheets required if the transmitted intensity is to be more than 50% of the original intensity?

(c) What is the minimum number of sheets required if the transmitted intensity is to be more than 65% of the original intensity?

Answer 1

a)

minimum number of sheets required = 2

b)

from malus law

I = Io cos^(2n) (90 / n)

for n = 1

I = Io cos^2 (90) = 0

for n = 2

I = Io cos^4 (90/2) = 0.25 Io

for n = 3

I = Io cos^6 (90/3) = 0.42 Io

for n = 4

I = Io cos^8 (90/4) = 0.53 Io

n=4 is the answer for 50% of original intensity

c)

from malus law

I = Io cos^(2n) (90 / n)

for n = 5

I = Io cos^10 (90/5) = 0.60 Io

for n = 6

I = Io cos^12 (90/6) = 0.65 Io

n=6  is the answer for 65% of original intensity