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hamdal
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I want to find out that what happens if we polarize a white light which has all of the wavelenghts of 400-700 (nm).Does it divide into colors?What happens to it?
sophiecentaur said:Unfortunately, the 'picket fence' analogy can be very misleading. It has to be presented very well if it is not to be taken wrongly. It always has to be stressed that the slots are not just 'selective' (only letting certain waves through) but they take one vector component of all waves that arrive. If the fence is merely 'selective' then it will only let an infinitesimally small fraction of the energy through as opposed to half the energy which is what we find with real polarisers.
The pictures in the above post are not good, in this respect; the bottom picture really does suggest that none of the slightly tilted wave would get through.
Also, there is no point in talking of "photons vibrating" in a particular direction. If this were a proper model then a polariser would be taking a fraction of the energy of any photon that is not perfectly aligned with the polariser's plane. We all know that photons have an energy value that is determined by the frequency so how could we only have a fraction of this energy? Why oh why do people seem to think that photons help in these arguments? It just shoots any explanation in the foot. (Even that picket fence argument manages to avoid photons - that is one small thing in its favour)
AbsoluteZer0 said:So the picket fence analogies are entirely useless?
Are you sure you mean Scattering?AbsoluteZer0 said:I believe you've mistaken Scattering with Polarization. Scattering is the splitting of white light into its component frequencies (red, orange, yellow, green, blue, indigo, and violet.)
http://en.wikipedia.org/wiki/Scattering
phinds said:I don't think the centaur said useless, the message was "misleading --- handle with care", which is a good message
EDIT: I think that as an explicitly non-technical ANALOGY, it is a helpful explanation for non-technical people.
I'm not sure what you read but the mechanism for that sort of thing is complicated and involves more than just birefringence. It involves the phenomenon of interference and the differing path lengths for the two rays through the medium. Certainly not the best thing to cut your teeth on in this topic. (Notice that the colours you get in examples like this are not the same as the 'rainbow'. They are more like oil film colours which are more 'garish' and unnatural looking.)hamdal said:No no no...I definitely didn't mean scattering,diffraction or any other things...I read that the colors appearing on a CD case is because the light polarizes and then Birefringence happens and some how we see colors...I'm trying to see why Birefringence and polarization gives us colors!
and by the way...when scattering, refraction or defraction happens the frequency stays the same, it's the wavelenghts that change!
acording to the Snell's law we have:
(V_1)/(V_2) =(λ_2)/(λ_1)
and we have:
V=fλ
so if:
(V_2)(λ_2)=(V_1)(λ_1)
then:
f_2=f_1
is not a 'result' ("then"); it's a starting boundary condition for phase continuity at the interface.then: f_2=f_1
sophiecentaur said:I'm not sure what you read but the mechanism for that sort of thing is complicated and involves more than just birefringence. It involves the phenomenon of interference and the differing path lengths for the two rays through the medium. Certainly not the best thing to cut your teeth on in this topic. (Notice that the colours you get in examples like this are not the same as the 'rainbow'. They are more like oil film colours which are more 'garish' and unnatural looking.)
btw, your final line
is not a 'result' ("then"); it's a starting boundary condition for phase continuity at the interface.
sophiecentaur said:I think you will need to say in more detail what you have read. It doesn't quite make sense to me. Birefringence will not, in itself, produce separation of wavelengths. You will get dispersion at an interface when the angle of incidence is not zero and, with a birefringent material, I guess you can expect the two rays to be dispersed differently and at different angles but, for parallel sided blocks, the 'prism' effect is minimal.
As I said earlier. This is a complicated scenario and you would need to describe more precisely what you want to know about it. If you want to understand how colours can be formed under different circumstances then it would be better for you to look at all possible mechanisms (dispersion, interference in thin films, diffraction by regular gratings etc.) and then see which one best describes what you have been seeing. This calls for some private study, I think, rather than 'question and answer' as, at the moment, your questions are not well defined enough to answer.
Polarization of white light beam refers to the process of aligning the oscillations of light waves in a specific direction, resulting in a beam of light with a specific polarization state. This means that the electric and magnetic fields of the light waves are oriented in a particular direction, which can affect the way the light behaves and interacts with other materials.
Polarization of white light beam can occur through various processes, such as reflection, refraction, and scattering. When light waves interact with a surface or material, they can become polarized as a result of the interactions between the electric and magnetic fields of the light waves and the atoms or molecules in the material.
There are three main types of polarization: linear, circular, and elliptical. Linear polarization occurs when the electric and magnetic fields of the light waves are aligned in a single direction. Circular polarization occurs when the electric and magnetic fields rotate around the direction of propagation. Elliptical polarization is a combination of both linear and circular polarization, where the electric and magnetic fields have both a direction and a rotational component.
Polarization of white light beam has various applications in science, technology, and everyday life. It is used in polarized filters for cameras and sunglasses, 3D movie glasses, and LCD screens. It also plays a role in the behavior of light in optical devices, such as microscopes and telescopes, and in the study of the properties of materials.
No, white light cannot be completely polarized. This is because white light is composed of a combination of different wavelengths and directions of polarized light. However, certain wavelengths or colors of light can be selectively polarized, resulting in a partially polarized white light beam.