Homework Help: Intensity of light passing through 3 polarizers

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1. Mar 8, 2017

ilovejava

1. The problem statement, all variables and given/known data
Three polarizing disks whose planes are parallel and centered on common axis. The directions of their transmission axes relative to the vertical are respectively: θ1 = 33° clockwise, θ2 = 21° counter-clockwise, and θ3 = 25° clockwise. A beam of light polarized along the vertical is incident onto the first polarizer with an intensity of I0 = 26 W/m². Calculate the transmitted intensity through all three polarizers.

2. Relevant equations
S=S0cos2θ

3. The attempt at a solution
I recognize that the light passing through the polarizers has already been polarized. To find the intensity of the light that passes through the first polarizer I used Malus' Law and used the angle 33°. I am not sure how to deal with the angles of the remaining two polarizers to find the total transmitted intensity through all three polarizers.

EDIT: The angle θ is the angle made between the axis of polarization of the light and axis of transmission of the polarizer. According to that logic I came up with the conclusion that

I0cos2(33)cos2(54)cos2(46)

54 is the angle made between 33° clockwise and 21° counter-clockwise, and 46 is the angle made between 21° clockwise and 25° clockwise

Last edited: Mar 8, 2017
2. Mar 8, 2017

Staff: Mentor

Good.

Do the same thing, only realize that after the beam passes through the first polarizer it is polarized in a new direction, given by the angle of the polarizer. Treat each passing the same way.

3. Mar 8, 2017

.Scott

The light incident on the seconds polarizer is also polarized - but not along the vertical axis. What is it's angel relative to the second polarizer?

4. Mar 8, 2017

Good!