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Jul
22
answered How does paper make sound when it is torn?
Jul
7
awarded  Commentator
Jul
7
comment How does paper make sound when it is torn?
If the paper is wet, it makes less noise when teared. So according to your explanation the bonds must get loosen, but I don't think there is any chemical reaction occurred when the paper gets wet. Because if we dry the paper again, it will be back as nothing happened before. How do you explain this?
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revised How does paper make sound when it is torn?
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Jul
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asked How does paper make sound when it is torn?
Jul
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comment What really cause light/photons to appear slower in media?
@anna v I don't get it why did you give me the link about resonance. I think it is normal for the phase velocity to exceed c, feynman's derivation: physics-gallo.blogspot.com/2008/08/… I already watched the feynman's lecture that you gave, imo it doesn't really relevant with what we were talking about.
Jul
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comment What really cause light/photons to appear slower in media?
@anna v i think pcr means the rayleigh scattering part of the diagram
Jul
4
comment What really cause light/photons to appear slower in media?
@ anna v and pcr I am guessing about this, Is it true that stimulated absorption/emission is like a "quantum" explanation for the "classical" driven oscillation? Because I think that it will agree with my classical understanding. @ anna v "IMO it must be higher order QED diagrams playing ball with the electric field of the atoms." I don't understand what do you mean "do you have a link that a difference between phase velocity and group velocity has been measured" I don't think that we need one, we can get the group velocity simply by calculating dw/dk of the function in the link that I gave.
Jul
4
comment What really cause light/photons to appear slower in media?
@ anna v I don't think it is necessary to be spontaneous emission, if it is spontaneous emission, then the emission will be directed in random direction right. If the emission is random, then the light would be heavily diffused, which is not what usually happen in daily life. In the real life case e.g light emitted by a lamp, the light's intensity can be considered as high. therefore it is still possible that the absorption emission process is primarily governed by stimulated absorption/emission. Is it true?
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comment What really cause light/photons to appear slower in media?
Actually I'm already using that point of view too, we can understand it more easily with phasor diagram. If the "new wave" is pi/2 degrees lag then if we add the old phasor with the new one, the result is like the old phasor gets rotated a little bit. So how do u explain for the case of negative index of refraction? Is it due to the same effect but the decrease in phase is larger than the phase that the light gains by travelling between atoms?
Jul
3
comment What really cause light/photons to appear slower in media?
I am actually interested in every wavelength, what you are saying is for long light's wavelength or small atoms spacing. In that case, I know that the photons will be scattered by atoms as a group(phonons). But for small enough wavelength, the light will only collide with one atoms at a time. And yet in practice, we didn't see any quantized the efect. I would like to hear your explanation for the case of short wavelength, a quantum mechanics explanation.
Jul
3
comment What really cause light/photons to appear slower in media?
ok seems like I don't have any problem with the classical explanation, but I'm still pretty confused about the absorption process. Would u mind to elaborate? where does the phase shift comes from quantum mechanically? and how do u explain for the case of negative index of refraction? Is it due to the same effect but the decrease in phase is larger than the phase that the light gains phase by travelling between atoms.