Question

Please answer quickly

Initially, unpolarized light with an intensity of 42.0 W/m2 is normally incident on three polarizers consecutively. Polarizer A is rotated - 20' with respect to vertical, Polarizer B is rotated +10° with respect to horizontal and polarizer C is rotated +35" with respect to vertical. What is the intensity of the light after passing through all three polarizers?

A 11.4 W/m2

B 12.1 W/m2

C 24.1 W/m2

D 12.9 W/m2

E 106 W/m2

Answer 1

When an unpolarized light passes through a polarizer, its intensity is given by:I=Io/2, where I is final intensity and Io is initial intensity.

Also, if a polarized light passes through a polarizer, I=Io (cos)^2 , where I is final intensity , Io is initial intensity and is the angle between polarized light and the polarizer.

So, for first polarizer, final intensity = 42/2=21 W/m2. (initialy light was unpolarized)

For second polarizer, final intensity = 21 [cos30]^2 = 15.75 W/m2.[=10-(-20)=30 degrees]

For third polarizer, final intensity = 15.75 [cos25]^2 = 12.9 W/m2.[=35-10=25 degrees]

So, option D is correct.