• Physics Discussion
    973 replies, posted
[QUOTE=Yahnich;39749453]today i spent 3 hours using matlab as a calculator to calculate the torque a magnetic field exerted fucking matlab you are the devil[/QUOTE] Matlab is pretty sweet, but then it's the only thing I've used. I've also used some stoneage version of Origin man it looked ugly.
LabView beats everything when it comes to evilness. [url]http://jshoer.wordpress.com/2007/08/03/why-i-hate-despise-detest-and-loathe-labview/[/url] I'd rather learn Assembler, because that would actually teach me something about the hardware I'm working with.
every other week our coursework is matlab-based, so we continually get practice at it also we're using it for our experiment this week. using a monochromator and detector to measure the transmission coefficient of gallium arsenide as a function of wavelength, from which we can calculate... something. band gap energy? and something else uh, I'd better get on that
[QUOTE=Number-41;39749917]LabView beats everything when it comes to evilness. [url]http://jshoer.wordpress.com/2007/08/03/why-i-hate-despise-detest-and-loathe-labview/[/url][/QUOTE] I can't agree even more. Our experiment runs on LabView VIs which are growing since the 90's. Nobody really knows what it is doing exactly in the internals and is has grown like cancer. Also it still uses legacy NiDAQ (totally outdated) for data acquisition (which forces our lab-control PC to use a 32bit OS - 8GB RAM for nothing) and a rewrite to NiDAQmx is out of question: A complete rewrite is easier than migrating the current system. Hell I hate LabView. Since we are on the like/hate topic about scientific software right now: I like mathematica for it's easy way to calculate simple stuff yet I hate it for it's syntax, auto-code-intending and bad modularity (one file for the whole code - To less flexibility for bigger projects). I like matlab because it has the flexibility mathematica is missing. Also it is a lot faster than mathematica in many cases. Anyway it lacks some functionality mathematica offers out of the box. Still it is superior. Then there is origin which I only use for plotting graphs. I never do fitting in it. I rather fit my data to a model in Mathematica and plot everything in origin. Why? Because it's easier that way since origin still feels like a compilation of several utils (I'm using origin 8.5).
oh my god it's aVoN hail [editline]28th February 2013[/editline] in our second year experimental module, we're using NIDAQ cards along with matlab for data acquisition
I'm using Origin 8.5 but I'll have/had to learn a shitton of new stuff since I switched to Geophysics for my Master.
[QUOTE=Killuah;39747610]Well technically I'd have to answer you that it's a derivative of the Fresnell Equations which in turn use energy conservation as a basic principle. [editline]28th February 2013[/editline] But maybe in laymans terms you could imagine a cube of glass. Now the light hits the cube on one surface and has one way or the other to cross it. It either stays it's projected path or changes its direction. And in the "denser" medium it tries to have a path as short as possible. [IMG]http://i.imgur.com/sXlfGe5.png[/IMG][/QUOTE] That's not an intuitive explanation, unless you're telling me light is making a conscience effort to take the shortest path. [editline]28th February 2013[/editline] Perhaps I should clarify a bit further. The reason why a medium is considered denser is because there are more electrons to absorb and reemit a photon. What about this process is changed by the shift in densities of electrons?
[QUOTE=Falubii;39747310]That doesn't do anything for me. I understand that it works, I want to know why.[/QUOTE] [URL="http://en.wikipedia.org/wiki/Fermat%27s_principle"]Just throwing this in here[/URL] [URL="http://physics.stackexchange.com/questions/466/what-is-the-mechanism-behind-the-slowdown-of-light-photons-in-a-transparent-medi"]more reading material[/URL] So far I only had it explained with Fermat and Maxwell's equations, no quantum mechanical explanation.
Nevermind, found this beautiful post courtesy of Physics Forums: [quote] Do Photons Move Slower in a Solid Medium? Do Photons Move Slower in a Solid Medium? Contributed by ZapperZ. Edited and corrected by Gokul43201 and inha This question appears often because it has been shown that in a normal, dispersive solid such as glass, the speed of light is slower than it is in vacuum. This FAQ will strictly deal with that scenario only and will not address light transport in anomolous medium, atomic vapor, metals, etc., and will only consider light within the visible range. The process of describing light transport via the quantum mechanical description isn't trivial. The use of photons to explain such process involves the understanding of not just the properties of photons, but also the quantum mechanical properties of the material itself (something one learns in Solid State Physics). So this explanation will attempt to only provide a very general and rough idea of the process. A common explanation that has been provided is that a photon moving through the material still moves at the speed of c, but when it encounters the atom of the material, it is absorbed by the atom via an atomic transition. After a very slight delay, a photon is then re-emitted. This explanation is incorrect and inconsistent with empirical observations. If this is what actually occurs, then the absorption spectrum will be discrete because atoms have only discrete energy states. Yet, in glass for example, we see almost the whole visible spectrum being transmitted with no discrete disruption in the measured speed. In fact, the index of refraction (which reflects the speed of light through that medium) varies continuously, rather than abruptly, with the frequency of light. Secondly, if that assertion is true, then the index of refraction would ONLY depend on the type of atom in the material, and nothing else, since the atom is responsible for the absorption of the photon. Again, if this is true, then we see a problem when we apply this to carbon, let's say. The index of refraction of graphite and diamond are different from each other. Yet, both are made up of carbon atoms. In fact, if we look at graphite alone, the index of refraction is different along different crystal directions. Obviously, materials with identical atoms can have different index of refraction. So it points to the evidence that it may have nothing to do with an "atomic transition". When atoms and molecules form a solid, they start to lose most of their individual identity and form a "collective behavior" with other atoms. It is as the result of this collective behavior that one obtains a metal, insulator, semiconductor, etc. Almost all of the properties of solids that we are familiar with are the results of the collective properties of the solid as a whole, not the properties of the individual atoms. The same applies to how a photon moves through a solid. A solid has a network of ions and electrons fixed in a "lattice". Think of this as a network of balls connected to each other by springs. Because of this, they have what is known as "collective vibrational modes", often called phonons. These are quanta of lattice vibrations, similar to photons being the quanta of EM radiation. It is these vibrational modes that can absorb a photon. So when a photon encounters a solid, and it can interact with an available phonon mode (i.e. something similar to a resonance condition), this photon can be absorbed by the solid and then converted to heat (it is the energy of these vibrations or phonons that we commonly refer to as heat). The solid is then opaque to this particular photon (i.e. at that frequency). Now, unlike the atomic orbitals, the phonon spectrum can be broad and continuous over a large frequency range. That is why all materials have a "bandwidth" of transmission or absorption. The width here depends on how wide the phonon spectrum is. On the other hand, if a photon has an energy beyond the phonon spectrum, then while it can still cause a disturbance of the lattice ions, the solid cannot sustain this vibration, because the phonon mode isn't available. This is similar to trying to oscillate something at a different frequency than the resonance frequency. So the lattice does not absorb this photon and it is re-emitted but with a very slight delay. This, naively, is the origin of the apparent slowdown of the light speed in the material. The emitted photon may encounter other lattice ions as it makes its way through the material and this accumulate the delay. Moral of the story: the properties of a solid that we are familiar with have more to do with the "collective" behavior of a large number of atoms interacting with each other. In most cases, these do not reflect the properties of the individual, isolated atoms.[/quote]
Why isn't there "Mathematicians Chat" anymore?
[QUOTE=Bradyns;39759007]Why isn't there "Mathematicians Chat" anymore?[/QUOTE] It had over 1,000 posts.
feels good getting out of the lab an hour early with data so good that your supervisor says "uh oh, that data actually looks good. that shouldn't happen in experimental physics" for anyone wondering we were basically replicating [url=http://academic.reed.edu/physics/courses/Physics332.s13/pdf/Optical_Bandgap.pdf]this experiment[/url] using only gallium arsenide, not silicon
I've had experiments where having the correct order of magnitude on a value was satisfactory :v: Man they make undergrads do so much useless shit (even with experimental setups that are used for actual research)
[QUOTE=Number-41;39762115]I've had experiments where having the correct order of magnitude on a value was satisfactory :v:[/quote] when this happens to you on a weekly basis, it makes it absolutely thrilling to get to within 2 significant figures of the expected value. it's just such a good feeling when an experiment gives precise data, especially when it's all automated using code you wrote yourself. [quote]Man they make undergrads do so much useless shit...[/QUOTE] truth
I'd have to explain the principles of a Hertz antenna to you for that but it's not intuitive either and I am on my phone so maybe you wanna Google fermat's principle instead. [editline]1st March 2013[/editline] ffs why did I miss all these posts what is happening [editline]1st March 2013[/editline] Yeah so imagine the point the light hits the glass as an infinitely small antenna.
Since google isn't helping, what would happen if something gets teleported (on earth)? I understand that a portion of air gets teleported with it, but what happens if matter gets inside matter? and the patch of vacuum where our "something" once was?
[QUOTE=qwerty000;39786781]Since google isn't helping, what would happen if something gets teleported (on earth)? I understand that a portion of air gets teleported with it, but what happens if matter gets inside matter? and the patch of vacuum where our "something" once was?[/QUOTE] nothing has been teleported like that ever, so nobody knows. Pauli exclusion principle might throw a fit if matter got into matter though (or cause a huge explosion), and as for the patch of vaccum: [URL]http://what-if.xkcd.com/6/[/URL]
[img]http://i.imgur.com/bUxy2ov.gif[/img] Two questions. What's the term or phenomenon occurring that results in that ring forming? I know it also happens with fire and water. The second being how is he directing that ring with his hand?
Vortexing.
I was wondering yesterday, could you, in practice, increase the effective yield of a railguns shot by placing a small sub-critical rod of uranium or plutonium into the centre of the slug? I was thinking on impact with a solid enough target the slug, and hence the sub-critical fissile core might get compressed (pancaked, if you will - imagine a car slamming into a cliff face head on at like 200 km/h and you'll get what I mean) enough to become a critical mass. If it worked, the resulting explosion would have energy supplied from both the kinetic energy of something travelling at several km/s and the nuclear energy of a small amount of fissile material.
[QUOTE=sltungle;39806878]I was wondering yesterday, could you, in practice, increase the effective yield of a railguns shot by placing a small sub-critical rod of uranium or plutonium into the centre of the slug? I was thinking on impact with a solid enough target the slug, and hence the sub-critical fissile core might get compressed (pancaked, if you will - imagine a car slamming into a cliff face head on at like 200 km/h and you'll get what I mean) enough to become a critical mass. If it worked, the resulting explosion would have energy supplied from both the kinetic energy of something travelling at several km/s and the nuclear energy of a small amount of fissile material.[/QUOTE] generally fissile stuff goes critical when the critical number of neutrons are reflected back into the reaction for it to be self-sustaining, as a [I]chain reaction[/I] you'd have to balance the plutonium very carefully - make sure it was shielded by the right amount of metal so that it would go critical just when it hit and not when you were loading it see: [URL="http://en.wikipedia.org/wiki/Demon_core"]demon core[/URL]
Urgh, me and a mate write the report in LaTeX, and the third dude does his part in Word whyyyy He shouldn't be such a lazy piece of shit and just go and learn it already (we even had a compulsory course ffs), it really isn't that much harder if you get the hang of it (I'm getting worse at Word than at LaTeX :v: ) Thank god its mainly text, so converting it shouldn't be that much of a problem.
[QUOTE=Eltro102;39811288]generally fissile stuff goes critical when the critical number of neutrons are reflected back into the reaction for it to be self-sustaining, as a [I]chain reaction[/I] you'd have to balance the plutonium very carefully - make sure it was shielded by the right amount of metal so that it would go critical just when it hit and not when you were loading it see: [URL="http://en.wikipedia.org/wiki/Demon_core"]demon core[/URL][/QUOTE] The demon core in no way applies to what I'm talking about. It was ALWAYS subcritical under its own geometry. The only reason it ever went critical was because neutron reflectors were placed around it effectively increasing the nuclear cross section. What I'm talking about is, in principle, similar to the operation of an implosion type nuclear weapon. A sub-critical mass of some radioisotope is compressed, increasing its density which in turn increases the nuclear cross section resulting in runaway nuclear fission. In an implosion type nuclear weapon this compression is supplied by a shell of conventional explosives placed around a sub-critical sphere of your radioisotope of choosing, however what I'm wondering is if enough linear deformation would occur to a railgun round on impact to cause a sub-critical rod of fissile material in it to go super-critical.
Learnt these in our lecture last night: [IMG]http://latex.codecogs.com/gif.latex?\Delta%20x\Delta%20\rho%20\leq%20\frac{h}{2\pi}[/IMG] [IMG]http://latex.codecogs.com/gif.latex?\Delta%20E\Delta%20t%20\sim%20\frac{h}{2\pi}[/IMG] Quarks today! [IMG]http://www.giraffeboards.com/images/smilies/sa-added/emot-engleft.gif[/IMG]
[QUOTE=Number-41;39813478]Urgh, me and a mate write the report in LaTeX, and the third dude does his part in Word whyyyy He shouldn't be such a lazy piece of shit and just go and learn it already (we even had a compulsory course ffs), it really isn't that much harder if you get the hang of it (I'm getting worse at Word than at LaTeX :v: ) Thank god its mainly text, so converting it shouldn't be that much of a problem.[/QUOTE] LaTeX is pretty shit IMO. Word does everything you need it to if you're competent; LaTeX requires additional learning that adds little. I have to do LaTeX for some stuff and it endlessly pisses me off.
[QUOTE=Bradyns;39819175]Learnt these in our lecture last night: [IMG]http://latex.codecogs.com/gif.latex?\Delta%20x\Delta%20\rho%20\leq%20\frac{h}{2\pi}[/IMG] [IMG]http://latex.codecogs.com/gif.latex?\Delta%20E\Delta%20t%20\sim%20\frac{h}{2\pi}[/IMG] Quarks today! [IMG]http://www.giraffeboards.com/images/smilies/sa-added/emot-engleft.gif[/IMG][/QUOTE] The energy-time uncertainty principle is an incredibly interesting notion to me. You can 'borrow' energy from the vacuum as long as it's returned in a time frame that satisfies the energy-time uncertainty principle. Generates a lot of interesting hypothetical scenarios (as well as actual, legitimate, real ones).
Delta rho? No h bar? What is this unconventional shit.
Isn't it like this? [IMG]http://latex.codecogs.com/gif.latex?\Delta%20x%20\Delta%20\rho%20\geq%20\frac{h}{4\pi%20}[/IMG]?
[QUOTE=Cooty;39819363]LaTeX is pretty shit IMO. Word does everything you need it to if you're competent; LaTeX requires additional learning that adds little. I have to do LaTeX for some stuff and it endlessly pisses me off.[/QUOTE] You have no patience
Might point that out to the lecturer.. I've known it as (hbar/2). Hmmm.
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