PLease help with polarizer/intensity question

  • Thread starter Sgtsloth
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In summary, the equation Itrans = I0 Cos2θ is used to calculate the intensity of light after it passes through two polarizers at different angles. In this conversation, the speaker uses this equation to find the intensity of light after passing through two polarizers at angles of 30 and 60 degrees. The first calculation results in an intensity of 0.75, which is then used as the new I0 for the second calculation. This results in an intensity of 0.1875, which corresponds to answer choice B. There is some discussion about using 30 or 60 degrees for the second calculation, but the speaker ultimately agrees with the use of 30 degrees.
  • #1
Sgtsloth
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So I know the equation:

Itrans = 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.
 
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  • #2
I agree with you.
 
  • #3
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
 
Last edited:
  • #4
Pharrett said:
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?
 
  • #5
Anyone else want to chime in, I still don't know which is correct.
 
  • #6
Sgtsloth said:
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.
 
  • #7
TSny said:
B is the right answer. Your analysis of using 30 then 60 degrees is correct.
Thank you
 

What is a polarizer and how does it affect intensity?

A polarizer is an optical filter that allows only light waves vibrating in a specific direction to pass through, while blocking all other directions. This filtering process reduces the intensity of light by only allowing a portion of it to pass through.

Why would someone use a polarizer?

A polarizer is commonly used in photography to reduce glare and reflections from non-metallic surfaces, such as water or glass. It can also enhance colors and contrast in certain situations.

How does the angle of a polarizer affect intensity?

The angle at which a polarizer is placed in relation to the light source and the object being viewed can significantly affect the intensity of light passing through. When the polarizer is perpendicular to the source of light, it blocks more light than when it is parallel to the source.

Are there different types of polarizers?

Yes, there are two main types of polarizers: linear polarizers and circular polarizers. Linear polarizers only allow light waves vibrating in a specific direction to pass through, while circular polarizers also have a quarter-wave plate that converts linearly polarized light into circularly polarized light.

How can I determine the optimal placement of a polarizer?

The optimal placement of a polarizer depends on the specific situation and the effect you are trying to achieve. Experimenting with different angles and orientations can help determine the best placement for your desired outcome.

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