Light and Absorptive polarizers

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In summary, the experiment with three polarizers at 45 degree angles to each other shows that polarized light can be transmitted when the filters are at 45 degrees to each other, but not when they are at 90 degrees. This is due to the transverse nature of light waves and the absorption of photons in certain planes by polarizing material.
  • #1
PenKnight
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Homework Statement



I was thinking about the 3 polarizers experiment where you have them angled 45 degree to each other and the first and third are perpendicular.

With 2 polarizer angles 90 degree to each other, no light passes through.
But with a third one inserted between them at a angle of 45 to the 1st and 3rd, light can pass through at a lower intensity.

I like to ask why?

Homework Equations



none.

The Attempt at a Solution



With 2 polarizer angles 90 degree to each other, no light passes through.
But with a third one inserted between them at a angle of 45 to the 1st and 3rd, light can pass through at a lower intensity.

I'm pondering on the why this happens. I've read a little bit of how the polarizers work. The electromagnetic waves must be perpendicular to the length of the metal grating so that it can pass through with a little loss of energy. Is this correct?

Secondly would diffraction have any part in the explanation?
Because I'm thinking the light in the one direction is diffracted. With the 2 polarizers, the interference pattern is absorbed by the 2nd polarizers, since all the light is parallel to the metal grating. But when a new polarizer is inserted between them, the light is firstly diffracted in a new direction through the 2nd polarizer which can pass through the 3rd lens?

This makes me wonder about another question.
Was the double slit experiment performed with monochromatic polarized light? Does it make a differences?

Thanks for your help
 
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  • #2
PenKnight said:
I'm pondering on the why this happens. I've read a little bit of how the polarizers work. The electromagnetic waves must be perpendicular to the length of the metal grating so that it can pass through with a little loss of energy. Is this correct?

No, that is not it.
Secondly would diffraction have any part in the explanation?
none, whatsoever.

Polarization and diffraction are completely different phenomena.

Polarization has to do with the transverse nature of light waves. Photons are an oscillation of electric and magnetic fields. THe direction of this oscillation is perpendicular to the direction in which the photon travels. Normal light is composed of many photons oscillating in random planes (up-down side-to-side, cross-ways). When transmitting through polarizing material, those photons oscillating in a certain direction will be absorbed by the material.

Those photons that oscillate cross-ways will have a portion of their energy absorbed such that all the light that transmits will be oscillating in one plane only. If the middle polarizer is put in at 45 degrees, then a portion of the polarized light will be transmitted such that the transmitted light is now in a 45 degree plane. The third filter is 45 degrees (not 90) to the second, so a portion of that light will be transmitted.
 
  • #3
Dear student,

Thank you for your question. The phenomenon you described is known as Malus' law, which states that the intensity of polarized light passing through a polarizer is proportional to the cosine squared of the angle between the polarization direction of the light and the polarizer. In other words, when the angle between the polarizer and the polarization direction of the light is 90 degrees, no light will pass through.

To understand why inserting a third polarizer at a 45-degree angle between the first and third polarizers allows some light to pass through, we need to consider the properties of polarized light. Polarized light is composed of electromagnetic waves that oscillate in a specific direction, called the polarization direction. When light passes through a polarizer, it only allows waves with a certain polarization direction to pass through, while blocking waves with other polarization directions.

In the case of the three polarizers experiment, the first polarizer only allows waves with a vertical polarization direction to pass through, while the third polarizer only allows waves with a horizontal polarization direction to pass through. When the second polarizer is inserted at a 45-degree angle, it allows some of the light to pass through because it is oriented at an angle between the vertical and horizontal polarization directions. However, since it is still blocking some of the waves, the intensity of the light passing through will be lower than if there were no second polarizer inserted.

Diffraction does not play a role in this explanation, as it is a phenomenon related to the bending of light around obstacles or through small openings. In the three polarizers experiment, the light is not being bent or diffracted, but rather being selectively filtered by the polarizers.

To answer your question about the double slit experiment, it was not performed with polarized light. However, polarized light can be used in the double slit experiment, and it does make a difference in the interference pattern observed. This is because polarized light has a specific direction of oscillation, which affects the interference pattern produced by the two slits.

I hope this helps clarify your questions. If you have any further inquiries, please do not hesitate to ask.

Best regards,

 
  • #4

Dear student,

Thank you for your questions regarding polarizers and their behavior in the 3 polarizer experiment. You are correct in your understanding that polarizers work by allowing only electromagnetic waves with a certain orientation to pass through, while absorbing or blocking waves with other orientations. This is due to the alignment of the molecules or particles within the polarizer material.

In the case of two polarizers at 90 degree angles, no light can pass through because the orientations of the molecules in the first polarizer block all of the light, and the second polarizer is oriented in a way that cannot allow any light to pass through. However, when a third polarizer is inserted at a 45 degree angle, some light can pass through because the orientation of the molecules in the third polarizer allows some of the light to pass through at a lower intensity.

As for your question about diffraction, it is not a factor in this particular experiment. Diffraction occurs when light encounters an obstacle or opening that is on the same scale as its wavelength. In the case of polarizers, the spacing between the molecules is much smaller than the wavelength of light, so diffraction does not play a role.

To answer your question about the double slit experiment, it was indeed performed with monochromatic polarized light. This was important in order to control for any interference patterns caused by different wavelengths of light. However, the principles of diffraction and interference are still the same for polarized light.

I hope this helps to clarify some of your questions. Keep up the curiosity and critical thinking!
 

1. What is a light polarizer?

A light polarizer is a device that filters out specific light waves, allowing only polarized light to pass through. It works by blocking certain directions of light vibrations while allowing others to pass through, resulting in a polarized light beam.

2. How does a polarizer work?

A polarizer works by using a material with aligned molecules that can absorb or reflect light based on its direction of vibration. This material is typically a thin sheet of special polymers or crystals that are arranged in a specific way to create a polarizing effect.

3. What is the difference between a polarizer and an absorptive polarizer?

A polarizer and an absorptive polarizer both work to filter polarized light, but they do so in different ways. A polarizer blocks certain directions of light vibrations, while an absorptive polarizer absorbs all light vibrations except for the desired polarization.

4. What are some common applications of polarizers?

Polarizers have a wide range of applications, including photography, LCD screens, sunglasses, 3D glasses, and scientific experiments. They are also used in various optical instruments, such as microscopes and telescopes, to reduce glare and improve image quality.

5. Can polarizers be used to block all light?

No, polarizers can only block specific directions of light vibrations. They cannot block all light as some light waves may still pass through the polarizer. However, multiple polarizers can be stacked together to reduce the amount of light passing through, resulting in a darker image or complete darkness.

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