Question

With 5 mW of light of an unknown polarization incident on a linear polarizer, you measure no light after the polarizer. If you put another linear polarizer before the one used above with its pass axis oriented 60° with respect to the other, how much power should you measure? Would your answer be different if the second polarizer was placed after the first polarizer?

Answer 1

part a)
leT po = 5 mW

from the givan data the angle between pass axis and incident light of polarization axis is 90 degrees.

because, P = Po*cos^2(theta)

0 = Po*cos^2(theta)

==> cos(theta) = 0

==> theta = 90 degrees

when you put another linear polarizer before the one used above with its pass axis oriented 60° with respect to the other,

power transimtted through first polarizer,

P1 = Po*cos^2(30)

power transmitted through second polarizer,

P2 = P1*cos^2(60)

= Po*cos^2(30)*cos^2(60)

= 5*cos^2(30)*cos^2(60)

= 0.9375 mW <<<<<<<<<------------------Answer

part b) yes.
If the second polarizer was placed after the first polarizer,

power transimtted through first polarizer,

P1 = Po*cos^2(90)

= 0

so, power transmitted through second polarizer,

P2 = P1*cos^2(60)

= 0*cos^2(60)

= 0 <<<<<<<<<--------------------Answer