Talk:Longitudinal wave

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[edit] Magnetic Formula

As written, this is nonsense, and I have yet to find a singe peer reviewed article by this Robert Bass. So I believe this should be removed Salsb 8 July 2005 14:46 (UTC)

Not everything in wikipedia needs to be from a peer reviewed journal. I have a copy of Bass's work via the scientific and enginnering library I am at. -Anon

Can you point out the exact "nonsense"? Otherwise it should stay. It's referenced and I have a copy of the references right in front of me. This is the 1st half of Bass's work. He goes on to delineate the a multipole expansion (analogous to the laurent series). Salsb, just because you don't know about it and/or it's not in a "peer reviewed" article, doesn't meant it shouldn't be on wikipedia. -Anon

The equations are written here produce a magnetic field which is identically zero. Prehaps it would be better to write a separate article on Bass' theory, which can expound on it in more detail. As far as being referenced, I would say the credibilty of the references is important Salsb 8 July 2005 15:20 (UTC)

The equations produce a "force free" magnetic field. Bass' work bleiongs here, as it is about the longitudinal waves. The credibilty of the references? Go get Bass's paper. It's reputable. -Anon

Ah, I see, as for the equations, if you are trying to reproduce the equations which give rise to the force-free magnetic field -> which BTW is called that becase of the neglect of the force from the gas pressure -- these aren't quite right. It looks like you are mixing up the A's as the fourier coefficients with the vector potential A(r). I don't have time to write the equations out at present, but I do hope to add them to the force free magnetic field later. Salsb 8 July 2005 15:57 (UTC)

Your equations still make no sense as written, but I realized that your discussion around force free magnetic fields was in reference to plasma waves, as your first reference makes clear. So I clarified it. Although if you read the second reference, it is relevant for force-free magnetic fields, as possibly the first application of them to sunspots. There are no discussions of longitudinal waves in there. Though plasma waves are usually considered separately from electomagnetic waves, because it usually the fluid oscillations which give rise to waves. Salsb 8 July 2005 17:26 (UTC)

Since some of the sections under electromagnetic waves appear to be on plasma physics --plasma waves and force-free magnetic fields -- and the equations credited to Bass are erroneous; I am revising this section. I will add the appropriate equations, eventually, to the 'force-free' magnetic field entry. I also revised the references section to include some reputable textbooks, in which you can find the discussions of both maxwell's equations and basic plasma physics Salsb 8 July 2005 23:01 (UTC)

I'm going to have a go at cleaning the article up a bit as well - hope I don't step on your toes. SeventyThree 9 July 2005 14:13 (UTC)

No problem, please help! Salsb 9 July 2005 17:42 (UTC)

The waves in plasma link is nice. I was going to write an article on them. I'm glad to see that there alread is one Salsb 9 July 2005 17:03 (UTC)

It's sad to see that the staements by Heaviside have been removed. No wonder physics students I've talked to are messed up, because professors like Salsb disreguard information by the likes of Heaviside.

The information by Bass should be in here. I'll radd him as a further reading.

Dear Anon -- I removed your edits for the following reasons

1) While you did correctly extract several paragraphs from Heaviside's work, you neglected to note:

A) Heaviside's points out throughout his work that there is no reason to suspect that there are such longitudinal electromagnetic waves, and good reasons to think that there are no such waves

B) After developing mathematical formulas for longitudinal waves, he then spends several pages showing that these waves are physically impossible.

C) At the end, he says we are back to maxwell and his transerve waves.

So a full reading of Heaviside's work shows the opposite of what it was included for, and is only of interest for the history of the development of electromagnetic waves

2) your representation of Bass' work previously was mathematically incorrect before, and doesn't make much sense as written, as it appears to contradict your reference to Heaviside, as well as standard texts in electromagnetism, for which I provided two standard references: one at the basic undergrad level, and one at the introductory graduate level.

3) a reference to force-free magnetic fields is confusing plasma waves with electromagnetic waves.

I did, however, include a mention of guided waves, and another editor helpfully included a link to waves to plasma, as you might be thinking of them Salsb 19:17, 11 July 2005 (UTC)

The relevant portions of Heaviside's work was cited. Though Heaviside's doubted that longitudinal electromagnetic waves existed, there are such waves in nature. It should be noted that Heaviside thought that these were physically impossible, but they do exist.

Bass' work isn't mathematically incorrect. The portion included was only the first half of the paper. It was, though, an alternative to the references of Heaviside.

longitudinal plasma waves and longitudinal electromagnetic waves are similar and should be discussedc here. A plasma wave basically is a medium saturated by electromagnetic waves.

I won't readd the information though. I will readd the reference you removed and NPOV the further reading. -Anon

A few things to note:

It appeared to me that your straight inclusion of Heaviside's work missed his point, in which he was attempting to generalize Maxwell's equations -- in an attempt to reconcile Helmholz's and Maxwell's work -- and he showed that one could not have longitudinal waves in a vacuum or a homogenous medium. Also he was not considering either plasmas or guided waves; as an expert in guided waves he would have known better. Note also, the appearace of longitudinal waves in such a case does not in anyway contradict maxwell's equation. In fact to obtain the waves, you use maxwell's equations -- see either the texts I referred you to.

Note I said Your presentation of Bass' work was incorrect. I suspect you were trying to write down equations for force-free magnetic fields, and making a mistake as noted above. Incidently, this would not be Bass' work as such, rather a conventional approximation.

Given the differences in reputation between the sources: standard texts, journal articles vs an unpeer-reviewed paper, it would be important to follow the anti-gravity article and indicate that Bass' work is not considered main-stream {which in of itself does not make it wrong, but we can lead it to the reader to decided whether to trust a non-peer-reviewed paper}

I still do not believe it is neccesary to include force-free magnetic fields, as they are the static magnetic fields resulting from a specific approximation. They also can vary spatially in a transverse or longitudinal manner , or neither.

I wrote what I hope is a compromise text, although I did not change the Bass reference.Salsb 20:40, 11 July 2005 (UTC)

[edit] Patent

The patent here is using longitudinal in a much difference sense than the rest of the article. Longitudinal is refering solely to the direction of propagation relative to the bore axis in a putative oil well. So longitudinal means that the wave is moving in the direction of the well axis; not that the electromagnetic waves have vibrations along the axis of propagation. Salsb 21:26, 11 July 2005 (UTC)

[edit] Maximum velocity of longitudinal waves.

A I correct that (in contrast to transverse waves) the maximum velocity of propagation cannot exceed the individual maximum velocities of the particles transmitting the wave. If this is correct, them em waves in plasma must travel very slowly cf the speed of light. Is that true?--Light current 16:48, 31 July 2006 (UTC)