How Does Light Intensity Change Through Multiple Polarizers?

[Sgtsloth]

So I know the equation:

I_trans = I₀ Cos²θ

Since this light starts out as polarized, there is no need to cut it in half like you do for unpolarized light. So I did the equation through the first polzarizer, using 30 degree as my angle, and came out with I=0.75

Now I used that 0.75 as my new I₀ as the light went through the 2nd polarizer, this time I used 60 degrees as my θ and I got 0.1875, which would be B.

However, I saw the same problem elsewhere where the guy got D) as the answer because he used 30 for θ instead of 60.

 

[blue_leaf77]

I agree with you.

 

[Pharrett]

edit: I didnt notice the opposite axis of the second one, I would say you are correct in your first assumption and I agree with the rest of the posters. use 30 then 60

 

[Sgtsloth]

Since you have 2 polarized sheets at 30 degree I would use 1(cos30^2)^2

That gives 0.5625, can you explain WHY you would use 30 degree for the second polarizer when the axis is 60 after the coming out of the first one?

 

[Sgtsloth]

Anyone else want to chime in, I still don't know which is correct.

 

[TSny]

Anyone else want to chime in, I still don't know which is correct.

B is the right answer. Your analysis of using 30 then 60 degrees is correct.

 

[Sgtsloth]

B is the right answer. Your analysis of using 30 then 60 degrees is correct.

Thank you