Talk:Bragg's law

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The merge is not necessary, since Bragg's Law or Bragg's condition can occur in other related areas, outside Bragg's diffraction. For example in Brillouin scattering [See for Example "Brillouin Scattering in Cubic Crystals" G.B. Benedek et al, Phys. Rev. 16,2,1966] Alektzin

I disagree, for the simple reason that it took me a long time to find Bragg diffraction and I instead spent my time milling around here, which is somewhat less useful. Sojourner001 00:24, 18 January 2007 (UTC)

[edit] Image:Loi de bragg.png

I think this image is not quite correct, since in the second diagram, the angle of incidence does not equal the angle of reflection. :) I'd've corrected that myself, but I don't have neccessary software... --Koveras 09:34, 5 November 2005 (UTC)

This image is fine. Diffraction is not like reflection. A-priori all angles are possible, but only those that give constructive interferences actually occur, as in the left image. The right image depicts the a destructive interferences, and therefore this will not be detected. --Hezy 22:50, 20 November 2005 (UTC)

The entire image is incorrect. The Bragg condition holds for a single photon, a second coherent wave in not required. Its like Young's Two Slit Experiment except more complicated.

Your assumption assumes that each "wave" represents one particle. Instead it could represent "one possible path for a particle", so, the image is not *a priori* incorrect; and it illustrates the point quite cogently. —The preceding unsigned comment was added by 137.131.130.118 (talk) 00:39, 24 January 2007 (UTC).

[edit] The Point May Have Been Missed

• I partialy agree with this anonymous fellow, above. For Bragg's law assumes that diffraction from crystal planes can be ragarded as the reflection of radiation off paralell planes. What Hezy says is very correct, "Diffraction is not like reflection. A-priori all angles are possible...", but in regard to a discussion about Bragg's Law, I'm sure diffraction is regarded the same as reflection. Bragg's Law is a model for diffraction, a simplification, that is not likley to hold in every case.

I do not however know that the Bragg condition holds only for a single photon, im sure it applies to waves equally. Indeed the wave needs to be monochromatic, but yes, there does not need to be a second coherent wave.

I make several recomendations:

1. This article should concentrate on Bragg's Law first, not theory that should be learned after comming to grips with Bragg's Law.
2. The image does need to be removed, as i believe that it does not show how Bragg's Law works in terms of lattice, or scattering, planes.
3. There should be a derivation to complement the Law so that a someone new to diffraction can understand it. At the moment i think only someone who has a prior understanding of the theory can follow it, and it should be made more accessible to lowwer levels.
4. I propose that is article can be re-written to accomidate the above

Honourable Crammer 04:22, 1 November 2006 (UTC)

Seconded - Thomson scattering occurs in all directions, but we have a whole separate article discussing that. Moving the geometric derivation to just after the historical section I think would make it more accessible. This goes double if we want to keep a separate article dealing with just Bragg's Law, with most of the crystallography and whatnot under Bragg Diffraction.

The Rayleigh image should then be moved to a 'more exactly microscopic' section following this. The loi_de_bragg image in my opinion needlessly complicates the article - if we show constructive interference, destructive interference leading to no measured reflection is implied; also, it digresses naturally into a discussion of finite crystallite size effects, which would be definitely off-topic.

Eldereft 16:30, 22 February 2007 (UTC)

What? No please don't remove this image, it's the only one that actually makes sense. I was taking a crystallography class, and I didn't quite understand the explanation of Braggs' law presented to me, but when I saw this image (and the succeeding one) I was able to understand it. As for the succeeding image, however, someone should really change it, since the 45 degree angles really make it look like AC' = BC, which results in the wrong equation all together.

I also think that the change Whiner01 made to the Angstrom unit was unnecessary. Although the unit of measurement is not in SI units, an angstrom Å, is still a unit of measurment commonly refered to in journals, text books, internet and class rooms when refering to distances in the order of atom spacings. But, at the same time, wikipedia is about making information more accessible to everyone, so perhaps it was warrented for that reason? i dont know. I shall think more clearly before placing a comment in the future. Honourable Crammer 13:12, 1 November 2006 (UTC)//