Misplaced Pages

Revision as of 17:10, 2 February 2007

Physics Unassessed

This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Misplaced Pages. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.PhysicsWikipedia:WikiProject PhysicsTemplate:WikiProject Physicsphysics ??? This article has not yet received a rating on Misplaced Pages's content assessment scale. ??? This article has not yet received a rating on the project's importance scale.

Template:FAOL

Oversized .GIF

Anyone else annoyed by the 6mb animated GIF? While it is effective at demonstrating a point, isn't there something that can be done about such a massive bandwidth hog? 60.224.44.222 08:08, 19 August 2006 (UTC) (can't be bothered signing in)

To Canberra-based user in Australia who "can't be bothered" to sign in: (a not-too-effective way to get people interested in queueing up behind you on an issue). Anyway, no kidding on the 6 MB file size! I didn't want to visit this article or even link to it because it was so damn slow. Now fixed. I used two applications on a Mac to convert the file into a version that is 4.7% the size of the original, is indistinguishable from the original in visual appearance, and which loads much faster. This version also has an interframe delay of 40 ms (v.s. the original’s 100 ms). Including processing time for each frame, this new version advances from frame to frame in 45–50 ms (a frame rate of about 20–22.5 Hz on a typical computer), which yields a more fluid motion. Greg L 14:28, 4 October 2006 (UTC)

Is this an error?

"There is no energy gap for phonons" (under Dispersion Relation) - but then what about Phononic Crystals which do have energy gaps? - h2g2bob 11/11/05

I suspect you'll find they're photonic crystals... -- CYD

There are both, though phononic and photonic crystals are very similar (phononic crystals have gaps in the acoustic (long wavelength) dispersion curve I believe) - h2g2bob 12/11/05

You should also note that several devices have gaps within there phonon spectrums such as silicon nanowires and nanodots (See Applied Physics Letters, Volume 87, Article 231906 (2005) ) - shepplestone 4-6-06

Having researched and examined the topic further, I have deleted the above statement as it is incorrect. shepplestone 23-11-06.

Please elaborate

I have read this article a few times and still only have a vague concept of phonons. Can we get some more detail (and layman's explanations) on these sections:

"According to a well-known result in classical mechanics, any vibration of a lattice can be decomposed into a superposition of normal modes of vibration."

Can we link to an article about this rule, or give a short explanation if none exist?

"Secondly, we treat the potentials V as harmonic potentials, which is permissible as long as the atoms remain close to their equilibrium positions. (Formally, this is done by Taylor expanding V about its equilibrium value.)"

The link to screened in the sentence above this one helps explain it, but the link to harmonic oscillator doesn't really explain to me what a "harmonic potential" is.

"As we shall see in the following sections, any wavelength shorter than this can be mapped onto a wavelength longer than a."

This seems similar to aliasing in discrete-time sampled signal processing. If the analogy is close enough, should it be mentioned? Also, analogies to vibrations in strings would help me in particular, but I don't know how close these analogies are, and if they would give the wrong idea.

I guess the rest I don't understand simply because I don't know quantum mechanics... - Omegatron 14:26, Jul 21, 2004 (UTC)

I think some of these have been addressed, but the entry definitly still needs some work (I'll see what I can do ;-). I like the aliasing analogy, it's exactly right (the points where the atoms are placed act like the points (in time) where the analogue wave is detected in digital streams.) --H2g2bob 02:10, 16 December 2005 (UTC)

--- Would it be possible to add some stuff about non-equilibrium processes, like thermal conductivity??

Thermal conductivity has a seperate page within wiki

plasmon

correcting small erro

Shouldn't "k" be "k_sub_n" in the exponents of the two Fourier relations immediately following the "One-Dimensional Phonons" subheading? Marcusl 15:58, 15 February 2006 (UTC)

Phonons & sound

In my opinion the reference to the name of Phonons is wrong: Phonons do not give rise to sound in crystals, there is merely a resemblace in the process. Sound would assume frequencies at least remotely near the audable range, which is not the case with phonons (>8 orders of magnitude difference).

Billiard ball model of the atmosphere

If one models air and air molecules as a lot of billiard balls in constant chaotic motion, then how does sound propagate through air? Are phonons associated with nitrogen and oxygen molecules, as they are with metal molecules? It seems it would be sort of Rube Goldbergian (like the board game Mousetrap) for sound to be carried and transferred between so many billiard balls in constant chaotic motion, when one is speaking to someone across the room.

I have read that air molecules at room temperature move about as fast as a jetliner; and that the average path lenght of an air molecule at room temperature is less than a meter. User: McTrixie --71.124.219.87 17:20, 27 August 2006 (UTC)

Why?

It's easy to think of waves in a lattice, but I still don't see why they would qualify as a (quasi)particle. Presumably physicists invented/discovered phonons because they are a useful description of the world, but when do they behave like particles? —Ben FrantzDale 06:05, 19 January 2007 (UTC)

For instance in inelastic scattering experiments (Brilloiun scattering, Raman scattering, neutron scattering etc.) they behve like particles. User:Matthias_Buchmeier

Phonons = bosons?

Hello,

This article seemingly contradicts boson by stating that phonons are bosons with integer spin, whilst the boson article states that bosons are particles with integer spin. This would make phonons=bosons, where my understanding of phonons is that they are purely propagation modes, where bosons are actual particles (where the word particle makes sense in quanta.

My understanding is insuffificent to declare this as correct, but does anyone have a definitive answer? User A1 14:08, 29 January 2007 (UTC)

anything with integer spin is in a group called the boson's, anything with half integer spin is in a group called hadron's, hence everything is either a boson or a hadron, in quantum mechanics ANYTHING with energy is a wave and so has a frequency and everything with frequency is a particle. so people are hadronic particles! the simplest observable indication of which of these groups something is in comes from the fact that hadrons can't pass through each other, when bosons can, since classical waves, like vibration, can, they are always bosons.

Asplace 11:19, 2 February 2007 (UTC)

So would I be correct in saying that the integer spin comment in phonon is superfluous? User A1 14:07, 2 February 2007 (UTC)

well you could actually read that last sentence in the header as, phonons are bosons BECAUSE they have integer spin. which is the definition of a boson, but seems to me ok if you assume the reader needs to be told that.

However i'm not sure the whole of the second paragraph isn't redundant, its trying to explain some general principles of QM, not really specific to phonons, a reader might be better of clicking the link to quanta at the top and reading about QM/superposition etc. there. this description is not the clearest i've come across. for example "they acquire certain particle-like properties when the lattice is analysed using quantum mechanics" how can an analysis cause properties? QM came about because people were already seeing particular properties in waves and needed to explain them, put simply, QM invents the concept of a wave/particle and says every wave and every particle is one of these, and it was a mistake to ever of thought they weren't. of course the maths used before QM doesn't suddenly stop working, but has clearer applicability restrictions. 81.7.61.38 17:10, 2 February 2007 (UTC)

• Unassessed physics articles
• Unknown-importance physics articles
• Unassessed physics articles of Unknown-importance