Talk:Beer-Lambert law

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• Fellow annonymous editor, indeed a lot of people (myself included) are used to your notation for writing the equation. However, if you have not realzied, all those other equations on the article call absorbance α and optical path &l; - not only the equations, that neat diagram which would have to be re-edited if we would change the notation. Not to mention that anyone with minimal common sense will read the legend underneath the equations and immediately identify α with ε within ten seconds, even if they find it a bit odd at first. So, we shall take the easy way on this and avoid an endless discussion on mere names... I better stop here.--Duplode 03:36, 14 April 2006 (UTC)

Dr Bob, I'm not sure where you are from...but google beer lambert and mostly everyone in our World (Earth) uses A = ε b c.

Dr Bob...the reason we introduce other variables is because not everyone is like dr bob and some of us use different variables. : )

• No, you did not introduce other variables; you introduced other names for variables. If you call absorptivity α, ε or whatever you wish it's still absorptivity. Therefore there is no need of introducing more letters and causing additional confusion when there is a clear legend under the equations.--Duplode 07:50, 8 April 2006 (UTC)

Yes, but wouldn't it be better if we used standard IUPAC nomenclature "A = εcl" instead?

Does this make sense: "If concentration c is expressed in moles per unit volume, α is a molar absorptivity usually given in units of mol cm^-2?" Shouldn't it say in units of cm² mol^-1? Srnec 04:30, 16 February 2006 (UTC)

Dimensional analysis agrees with you, but perhaps there is some other error.--Srleffler 05:24, 16 February 2006 (UTC)

• That was just a simple error, it should be mol^-1 cm^-2. I've fixed it and also recast the law in terms of log10, since that seems to be the most common way the law is expressed (my lab spectrophotometers all work that way). This also makes it compatible with related articles in WP (e.g. optical density), and inconsitancy is bad. Unfortunately, in general optics it's also pretty common to see it in the exponential form, so some confusion is possible. --Bob Mellish 20:43, 16 March 2006 (UTC)

[edit] Transmittance

I think the article should more explicity explain the relationship beween absorbance and transmittance, or point to an article that does cover this. It is sort of in the article already (Ii/Io), but that wouldn't be clear to the uninitiated. ike9898 17:43, 14 March 2006 (UTC)

• Another observance about this page. With the italic font being used, the characters representing intensity (I) and distance (l) both look confusingly similar.

[edit] Derivation added

I've added a simple derivation of the law, with an explanation of the problem at high concentrations. I've used the notation in the previous section, although I do not like it - for reasons that others have already mentioned. It seems we're married to the notation used in the figure, and this is unfortunate. ike9898 - I added a line defining transmittance after seeing your comment.

This is actually my first contribution, and my first attempt at LaTex. The fonts don't look quite right, and I would welcome anyone attempting to clean it up.

Axewiki 12:51, 13 September 2006 (UTC)

I fixed some of the Tex, and removed the last paragraph. The law works even for high concentrations, because the thickness of the slab is dz which is infinitesimally small. For a slab of finite thickness, the chance that there will be an overlap decreases as the thickness of the slab decreases, until it is zero when the slab is infinitesimally thick. PAR 03:00, 14 September 2006 (UTC)

I am not familiar with the common notation for this law, but the article should be consistent. In the first part, base 10 and l is used:

while below, base e and is used

Thanks PAR - your Tex is much better. I also agree with your comment about consistency between base 10 and natural logs - I have fixed that. However, I must insist that the Beer Lambert law breaks down at high concentrations, and it does so for the reason I gave. Even the author of the first section on "Equations" mentions this point. In your 'talk' paragraph above, you mention that the slab becomes "infinitesimally thick". I think you meant "thin", but no matter, the breakdown has nothing to do with the calculus or the thickness of the slab, only with the likelihood that one molecule along the path of a photon eclipses another, making the second molecule "invisible" to whatever detector is measuring the transmitted light. This likelihood of such an eclipse increases with increasing concentration. Breakdown of the Beer-Lambert law at high concentrations is a universally recognized phenomenon that I routinely use as a teaching demonstration for students in my lab. Please don't take offense that I reinserted the final paragraph in this section.

Axewiki 16:05, 14 September 2006 (UTC)

[edit] Beer-Lambert Lambert and Beer laws

Beer-Lambert law is a conection of Beer law and Lambert law, so in the very first line is untrue information. Both are now historical, but...

the Lambert law states for that absorpction is proporcional to the ligtht path length,

the Beer law states for that absorpction is proporcional to the concentration of absorbing species in the material.

So if you have time to fix it, please do it. Probably it will need a minor changes in biographical articles about Beer and Labbert. --82.139.42.165 23:16, 25 September 2006 (UTC)