Wikipedia:Reference desk/Archives/Science/2007 April 21

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April 21

permanent magnet

i know that if you hold 2 permanent magnet in a position where they repulse each other for a long period they should demagnetize but i would like to know if , if you hold 2 magnet side by side with the poles parallel to each other would they demagnetize? clockwork fromage —The preceding unsigned comment was added by 216.113.99.57 (talk) 01:46, 21 April 2007 (UTC).

Permanent magnets always demagnetize, it's just a matter of time. Putting it in the presense of an opposing magnetic field will accelerate this process, though just how much is dependent on the type of magnet and strength of the magnetic field, and I'm not honestly sure how great the effect is. Holding magnets side by side with their poles facing the same direction accelerate the demagnetization, and holding them with their poles facing opposite directions will not. Again, I'm not sure how much this actually accelerates the demagnetization. Someguy1221 02:21, 21 April 2007 (UTC)

Well it seems I don't remember my E&M, some of what I said is true, I think...Permanent magnets can demagnetize in the presense of an opposing magnetic field. Further, a permanent magnet that has been artificially strengthened by being exposed to a very strong external field will gradually demagnetized due to its orginal state being entropically favored (I think). Ok, sure, my statement that they always demagnetize was a wee bit incorrect, but artificially strengthened ones will weaken (even if it takes hundreds of years). I'll slap myself if I'm still wrong. Someguy1221 03:44, 21 April 2007 (UTC)

I agree with Someguy1221: (1)left in a region of zero external field, a ferromagnet will gradually experience bulk demagnetization as thermal oscillations favor an increase in entropy. Note that individual grains (size governed by the coherence length, or whatever it is called in magnets) will remain ordered within themselves, but will become randomly oriented with respect to each other. (2) Two magnets aligned pole-to-pole such that they repel are in an energetically disfavored orientation. Left free to rotate, they will do so; if constrained, the individual moments will flip at a greater rate than if the other magnet were not present. I would not expect to observe this in a reasonable amount of time by clamping two refrigerator magnets together, though. Practically, I believe that it is nearly always cheaper to heat a material past its Curie temperature then cool it in the presence of a field than it would be to realign a ferromagnet using just a high magnetic field.Eldereft 07:09, 21 April 2007 (UTC)

Once upon a time a popular kind of permanent magnet was the horseshoe magnet, and these usually came with a "keeper", a piece of metal left across the poles of the magnet when not in use and without which, over time the magnet would deteriorate. —Steve Summit (talk) 12:52, 21 April 2007 (UTC)

i know you can demagnetise a magnet with an impact but if i need to put a magnet in something that will recive impacts (average 10 to 20 pounds), if i try to dampen the impact with a layer of rubber or something better would it be easy or at least possible to lower it enough to not any magnetic strenght?

plant metabolism acceleration

a horticolt friend of mine once told be that if you dig a tree oft of the ground with its roots for transplantation and you transport it with a car at high enough speed and do not cover up the leaves with a plastic sheet , the leaves will shrivel up because because of capi;ary action and the lack of any water for the roots to suck up

my question is would this mean that if plants and/or trees were put in a green house with a huge fan that would keep them constantly in high wind would this force the plants tosuck more water and maybe minerals from the ground and would this accelerate theyr metabolism therefore making them grow faster? clockwork fromage —The preceding unsigned comment was added by 216.113.99.57 (talk) 02:12, 21 April 2007 (UTC).

if you drive the car at high speed, the resulting high wind will blow of leaves and snap the branches. Plant growth will be limited by what is in short supply. This may be some mineral sucked up with the water, but could also be carbon dioxide, or water. It would be better to have appropriate humidity in the air and enough minerals in the soil, I suspect, trhan a high wind that can cause damage. If plants are moved around or brushed they tend to grow more stumpy. Look at plants growing on mountains or cliffs exposed to high wind and you will see natural bonzais. GB 10:13, 21 April 2007 (UTC)

There is a technique for making large plants, such as gourds, by "pumping" them with water. That is, water (with minerals) is injected into them to make them grow larger. I think of this as cheating, when it is used to create the "largest pumpkin" for a state fair, for example. The results also don't tend to be very edible, more a big sack of mineral water than what you would think of as a pumpkin. StuRat 16:54, 21 April 2007 (UTC)

Bile

Is there really such a thing as black bile and yellow bile? bibliomaniac15 04:01, 21 April 2007 (UTC)

No, there's only one kind of bile. Of the four humors, only blood has any actual physiological significance. - Nunh-huh 04:23, 21 April 2007 (UTC)

Does Humorism not answer this question? 75.138.84.159 04:20, 21 April 2007 (UTC)

And also, I hear bile described as a bitter fluid, but who took the time to taste other people's body fluids? bibliomaniac15 21:12, 21 April 2007 (UTC)

Tasting body fluids was a widely-used diagnostic method of medieval physicians. Urine was a favorite. I'm inclined to think, however, that the perception of bile as bitter arose from the taste in one's mouth when almost vomiting, the idea being that the bile rises to the gorge of one's throat. Perhaps confirmed by bile obtained by dissection/autopsy :). - Nunh-huh 08:14, 22 April 2007 (UTC)

Reference for Scientific Method

Does anyone know a reference ( book ) which I can use to research the scientific method ? Its very urgent , so I would appreciate any help .. Thank you . Hhnnrr 04:08, 21 April 2007 (UTC)

Thanks I found them in the article Hhnnrr 04:19, 21 April 2007 (UTC)

Whenever I see the scientific method mentioned, I invariably come to the conclusion that the people who write about it spend a lot more time thinking about science than doing science... -- mattb 05:00, 21 April 2007 (UTC)

Aerogel

I was reading the aerogel article and came upon this: Carbon aerogels are also extremely "black" in the infrared spectrum, reflecting only 0.3% of radiation between 250 nm and 14.3 µm, making them efficient for solar energy collectors. I was wondering are solar energy collectors refering to solar panels if so then would Carbon Aerogels be better than Silicon?67.127.166.90 04:45, 21 April 2007 (UTC)

I can't comment on aerogels in detail, but I don't think they exhibit any photovoltaic effect, which would rule out the relatively efficient optical-to-electrical energy conversion mechanism used by cheap silicon solar cells. I guess the implication is that the absorbed optical energy is converted into heat, which is also a usable energy form, though one that will probably be subject to more conversion loss. -- mattb 04:58, 21 April 2007 (UTC)

Carbon might be good at absorbing the energy (getting hot), but it re-radiates easily so doesn't tend to get really hot. See Selective surface. Polypipe Wrangler 07:51, 21 April 2007 (UTC)

But, a passive solar water heater, consisting of a clear tank of water with a carbon aerogel near the bottom, might be fairly efficient. StuRat 16:48, 21 April 2007 (UTC)

Probably more so than photovoltaic optical-electrical energy conversion followed by resistive electrical-heat energy conversion. You might even be able to effectively use both schemes if you circulate water in contact with your PV cells (which certainly heat up a good deal). -- mattb 03:59, 22 April 2007 (UTC)

Thanks!

Could anyone explain he mechanism by which two photon particles interact ? is the mechanism same for other bosons ?

what will happen if two photon particle of different energy level collide with one another ? —The preceding unsigned comment was added by 202.56.7.139 (talk) 08:39, 21 April 2007 (UTC).

Interesting question. In theory the wave functions will just linearilly add up and nothing else will happen, but that cannot be the whole of the truth. 84.160.246.10 08:44, 21 April 2007 (UTC)

If the photons have high enough energy, a particle and its antiparticle are produced. This could be and electron and positron but could also be other more exotic particles. This is the opposite of Annihilation. This only happens at gamma ray energies. This same effect limits the highest levels of energy of gamma rays tah could exist in the universe, as they will strike cosmic microwave background photons, which have low energy, but which are very dense. GB 10:20, 21 April 2007 (UTC)

The last part is just plain wrong, and the first part is confused. High energy photons can produce particles (including but not at all limited to electron/positron pairs), but ONLY in an interaction with another particle (one with mass, not with another photon), due to conservation of momentum. That's why the last part is utterly wrong. Well, that along with other problems, such as that photons don't "strike" other photons, and that photons are massless and therefore have no density, etc. Dougmerritt 23:11, 21 April 2007 (UTC)

Photons are bosons, thus, in a simplistic way, don't interact--or collide--with each other. (They just pass through each other.) Bosons do interact with fermions, however. When you are looking, for instance, at a white light source, you are not seeing "white" photons, but a balanced mix of photons of different wavelenghts from the visible spectrum. The fact that your eyes interprete this mix as "white" is only a physiological phenomenon. The underlying photons are unchanged. Tools like prisms can split them again.--JLdesAlpins 17:20, 21 April 2007 (UTC)

All true, but all of that about white light and physiology and prisms is utterly irrelevent to the question asked.

To start with a simple approximate answer, as JLdesAlpins said, photons are bosons and do not interact directly with each other. The simplest way to understand this is via classical physics, in which light is viewed as acting as a wave, not as consisting of particles. Observe ripples in a pond or sink; they pass through each other without interacting.

The quantum physics sense of considering light as being composed of photons which are "particles" in some sense should be viewed as an extra complication, not as a contradiction of the classical physics approximation. (You asked about collisions, not about e.g. the photoelectric effect or the quantization of atomic emissions.)

Photons are bosons, so as a first approximation, yes, bosons in general are like that.

The definition of the terms "boson" and "fermion" comes from the same thing that causes the two to behave differently, and it begins in a very simple way:

A boson obeys Bose-Einstein statistics, while a fermion obeys Fermi-Dirac statistics. (This turns out to hinge on the particle's spin; the former have integer spin, the latter have half-integer spin. This in turn leads fairly directly to explanations of how exotica such as lasers and superfluid helium behave, but that's a digression. It's also the single best issue to follow up on to really learn important qualitative things about fundamental physics.)

The word "statistics" here simply means, "how should something be counted?", which hinges on identity: the question of which particles are literally the same and which ones are different. Any given particle has a small list of associated characteristics (quantum numbers) that collectively specify 100% of its properties, including its actual identity -- there can be only one particle with exactly the same list of quantum numbers. If there were two, that would mean we didn't have the complete list of quantum numbers it takes to establish a particle's identity.

An electron is a fermion, and it has quantum numbers like spin and charge and mass and position and momentum.

All electrons have the same spin (1/2) other than orientation, the same charge, and the same mass, but other quantum numbers like position and momentum can (and must) vary between different electrons.

The fact that position is in the list means that no two electrons can be in exactly the same position in space-time if the rest of their quantum numbers are the same. That includes an electron in an orbital in an atom; a second electron in the same orbit must have some quantum number different than the first (typically its spin is reversed from the first, and since there are only two possible orientations for spin in this context, that means any third electron has to vary yet another quantum number, or else it can't share that orbital).

A photon is a boson (and has spin 1), and unlike fermions, its quantum numbers do not include mass and position, so any two photons can, in some sense, "occupy" the same position in space-time without the two actually being just one particle. This is both a true approximate answer to your question, but also obviously is somewhat self-contradictory, if you look at the way the word "position" was used in this paragraph.

That's because this is an area where things get very weird and unintuitive in quantum physics. It's not so weird if we switch back to the classical view of light being a wave, because then it's more obvious that waves don't have a pinpoint position (unlike our intuition about "particles"), and it is true in quantum physics that photons are not localized; they do not have a pinpoint position.

In thinking about position in regard to light, it's best to think of light being a wave, even though it's also true that it is useful to think of light as composed of particles when it comes to things like quantization of energy.

This does not mean that modern physics is confused about whether light is "really" a wave or a particle, it just means that ordinary intuitions do not apply, and so the subject seems somewhat confusing in certain regards until one actually studies mathematical quantum physics.

Even then, there are plenty of remaining mysteries in physics, but they're not quite the same ones that seem mystifying to the layperson. Dougmerritt 23:11, 21 April 2007 (UTC)

Explain me photon characterastics . how black-hole attract photon while photon is massless ?

does photon interact only with charged particles(electron) as in compton effect or photon interact with non-charged particles(nutrino) ? how nutrino passes through matter without interacting with it . —The preceding unsigned comment was added by 202.56.7.139 (talk) 09:23, 21 April 2007 (UTC).

Photons are attracted to black holes through the curvature of spacetime, see Bending of light. Not sure about the rest. Someguy1221 09:34, 21 April 2007 (UTC)

Just to clarify, it's not really attraction, just light following a curved inertial path...Someguy1221 09:35, 21 April 2007 (UTC)

To Someguy1221, why can't we denote the 180 degree bending of photon particles towards black hole as attraction, how this phenomenon is different from normal gravitational atttraction between two massive particles ? photon bends towards blackhole because of it's huge mass ; am i right?

To speak in a literal sense, it depends on what you mean by attraction. Attraction between particles typically implies the action of a force between them, which is illusionary in gravitational fields per general relativity. In truth though, you are right that photons are attracted towards black holes as much as anything else. My objection is merely over what to call it. Someguy1221 10:21, 21 April 2007 (UTC)

In theory, photons interact with neutrinos gravitationally, but of course nobody is currently able to measure that. Neutrinos are able to pass through matter with little interaction because (neglecting gravity) they only interact via the weak force; they have neither electric nor strong charge, and they don't have a magnetic moment. Icek 16:13, 21 April 2007 (UTC)

From the photon's perspective, its path is always straight. The photon, being massless, is not affected by the force of gravity (F=ma), therefore is not pulled by or attracted to the black hole. The photon only follows a "straight" line which lies in a "curved" space. If the "straight" line happens to venture inside the black hole's event horizon, then that means that "that" strainght line is somehow pointing toward the center of mass of the blackhole.--JLdesAlpins 17:31, 21 April 2007 (UTC)

Photons do have a mass, it's $\ m={\frac {E}{c^{2}}}={\frac {h\nu }{c^{2}}}$. They don't have a rest mass, though. 84.160.241.228 19:44, 21 April 2007 (UTC)

In modern physics, the term "rest mass" is no longer used at all, and the term "mass" ALWAYS means "rest mass". This has been true for decades. The only continuing use of the term "rest mass" is to help disambiguate when teachers are talking to students (and of course by journalists in popular science books/magazines, and of course the term never went away in popular usage by laypeople).

In that modern usage, it is considered bad form at best, and incorrect at worst, to talk about photons having mass. They do not. They have momentum. Dougmerritt 23:32, 21 April 2007 (UTC)

JLdesAlpins is correct, except for one unfortunate turn of phrase. It is not that "photons are not affected by the force of gravity", it is that, in General Relativity, gravity is not a force at all, period, unlike the other 3 fundamental forces. The curvature of space just makes it look like gravity is a force.

Early in the twentieth century, a fairly successful attempt was made to enhance General Relativity to do the same thing with the electromagnetic force: the 5-dimensional Kaluza-Klein theory handled electromagnetism has a property of a fifth dimension, and not as a literal force.

The other two remaining fundamental forces, the strong and weak nuclear forces, on the other hand, have never been 100% successfully reduced to a matter of geometry, but starting in the late 1960's, a partially successful attempt to do so was begun. Its roots lie in Kaluza-Klein, but has been hugely expanded.

That effort is known as "String Theory", so you can imagine that all this is a big deal, not a small one. :-)

One tidbit about GR that is very unintuitive, that helps illustrate that the difference between the force-approach and the geometry-approach can be enormous, not trivial: there are solutions to Einstein's fundamental GR equation in which local maximal curvature of space occur in a mass-free region (i.e. vacuum), rather than more intuitively centered about some mass. Mass and curvature are related, but nowhere near as directly as one might think. Weird stuff. Dougmerritt 23:32, 21 April 2007 (UTC)

black holes

How are black holes formed? Are they formed by spontaneous explosion of giant stars? —The preceding unsigned comment was added by 202.149.38.43 (talk) 09:46, 21 April 2007 (UTC).

Check out Formation of black holes. Many questions that are asked here can be answered simply by searching for the term in question on this very website. Someguy1221 10:03, 21 April 2007 (UTC)

To put this simply: A star is a very large and heavy thing - it has immensely strong gravity which is counteracted to some degree by the pressure of light and other radiation shooting out from it's core - the star is only as big as it is because the light is 'fighting' the gravity to keep it 'inflated'. Some stars eventually explode as supernovea - others do not. In that case - after an immense amount of time has passed - the star gradually runs out of nuclear fuel - less light comes from the star and there is less 'light pressure' to hold it up against gravity. Inexorably, as the fuel runs out, gravity starts to win and the star crushes itself beneath it's own weight. If the star is a fairly small one, then it crushes down to a "brown dwarf" - maybe the size of a large planet - that emits little or no light. If it's a bit bigger than that then the forces between the atoms of the star are not enough to resist it's immense gravity and the atomic nucleii are crushed together until the nucleii are actually touching - this is called a 'neutron star' - and it's very small (perhaps the size of a big city) - and incredibly heavy. But the very largest stars of all have so much gravity that even the nucleii can't withstand the forces - and the star crushes down smaller and smaller until it's a zero sized 'dot' - the gravity is still so strong that even light cannot escape if it gets too close to the star. Anything within that distance is therefore 'black' - hence 'black hole'. SteveBaker 16:16, 21 April 2007 (UTC)

Mixing of oxygen with LPG for easy melting

Hi!! I M working in a copper Industry. Im in the rod plant as a Quality control. Here for melting the cathodes we r using a furnace with some burner conected in it. We r mixing air and LPG for flame. Our LPG usage is high (its arround 40 kg/Mt). If we supplied oxygen (oxygen cylinders) with the LPG the heating rate will be more and there may be a reduction in LPG so let me know is it possible. If yes then how to implement it?? —The preceding unsigned comment was added by Sasthaanand (talk • contribs) 11:37, 21 April 2007 (UTC).

Unless it's currently not burning in the right condition (too little oxygen or something), I don't see how that would have an effect on the efficiency on the heater. You need oxygen and LPG in a specific ratio to burn it most efficiently, and it doesn't really matter much if that oxygen is coming from the air or from an oxygen cylinder. --antilived^{T | C | G} 11:52, 21 April 2007 (UTC)

Well, at one level, it matters a huge amount! Some burners (gas stoves, most handheld torches) are designed to burn a fuel using ordinary air as an oxygen supply. Others (oxy-acetylene torches, Saturn V main engines) are designed to use pure oxygen. So yes, you can get a hotter or perhaps "more efficient" flame by using pure oxygen. But any burner is designed for one oxidation method or the other -- conversion of a fuel/air burner to fuel/oxygen would not be a simple adjustment; it would involve a complete redesign and remanufacture of the burner.

A burner of either design does need to be adjusted properly, of course. If the fuel/air or fuel/oxygen ratio is not correct, the burner will not reach its desired temperature or efficiency. (Also it may be damaged, if the hot part of the flame recedes into the nozzles and overheats them.) Just about any burner allows the fuel supply, and perhaps independently the air or oxygen supply, to be adjusted so that the correct firing rate and oxidizer ratio is obtained. —Steve Summit (talk) 12:46, 21 April 2007 (UTC)

I'll note that a flame supplied with oxygen is almost always going to be hotter than the same flame supplied with ordinary air. You're not wasting heat warming up all that inert nitrogen, and your oxidizer and fuel can be concentrated in a smaller volume (no dilution by inert gases).

That said, I will agree emphatically with Steve's remark above—don't even think about supplying oxygen to a system that isn't designed for it without consulting an expert. Those smaller, hotter flames will tend to chew through your burner if it's not designed for the higher, more intense heat; that assumes that you can get the gas mix right to light it in the first place.

There are also safety issues to consider. Combustion proceeds much more rapidly under pure oxygen than under air. It's possible to ignite a number of metals in a pure oxygen atmosphere. Oxygen, unlike LPG, doesn't have an odorant added to warn you of leaks. If you want to switch over to generating high heat using large volumes of oxygen, you need to, again, consult an expert. TenOfAllTrades(talk) 13:25, 21 April 2007 (UTC)

What Ten Said. I didn't read the original question carefully enough -- you weren't thinking of actually trying this yourself, were you? This is why we occasionally read headlines like "Massive Explosion At Industrial Plant Kills 27, Leaves Hundreds Homeless", above an article in which we learn in paragraph 5 that "investigators believe that the explosion was caused by unauthorized modification of the plant's furnaces by untrained workers, in a misguided attempt to boost output." —Steve Summit (talk) 16:02, 21 April 2007 (UTC)

The traditional and somewhat more safe approach would be to preheat the air with the heat of the exhaust fumes by Countercurrent exchange. Oxygen only gives you a hotter flame and saves oyu the heating costs of the nitrogen contaied in the air along with the oxygen. Countercurrent exchange helps you to save energy. This too, should be done by an expert. 84.160.241.228 20:03, 21 April 2007 (UTC)

How expensive are oxygen cylinders? I susect the ROI of using oxygen isn't worth it. --Tbeatty 06:06, 23 April 2007 (UTC)

Myoglobin production and Brain oxygen storage

Peeps what process in the body regulates myoglobin ammounts and why does the brain lack any additional storage of oxygen?Bastard Soap 11:47, 21 April 2007 (UTC)

I guess compactness (equals signal speed) has priority over storage issues. 84.160.241.228 22:50, 21 April 2007 (UTC)

Never heard oxygen can be dangerous too? Too much and you get peroxide radicals that can do protein and DNA damage. --85.179.17.199 16:40, 22 April 2007 (UTC)

Myoglobin in the brain. Myoglobin can act as a scavenger of nitric oxide, which might cause a problem for the brain and use of nitric oxide as a signaling molecule. Hypoxia-inducible myoglobin expression in nonmuscle tissues talks about regulation of myoglobin expression and reports a form of myoglobin that is expressed in carp brain. See alao: Neuroglobin. --JWSchmidt 20:21, 22 April 2007 (UTC)

Boosting aerial/antenna strength

Is there a way I can increase the strength of my digital tv aerial/antenna (for a digital tv card for a laptop) as I can't currently pick up any digital tv (or radio) stations but I know folk in the same village, less than 1/4 a mile away, can. AllanHainey 12:06, 21 April 2007 (UTC)

Yes, you can get an aerial amplifier or "booster box". There is some discussion here (and elsewhere on the web). Something like this may work - cost is generally UK£10 or 15, so its worth a go (plus you may be able to take it back if it doesn't work :-). Take a look at the UK Government website for official info. --h2g2bob 13:54, 21 April 2007 (UTC)

They featured a home made arial on Brainiac: Science Abuse not long ago. It used a series of beer cans and cooking foil. Apparently it worked better than most shop bought arials and boosters... Think outside the box 14:04, 21 April 2007 (UTC)

You can increase your gain either with a better antenna or with an amplifier. If possible get the better antenna, because this can increase the SNR. An amplifier will amplify both signal and noise, and will introduce a bit of additional noise, so you have more gain, but a (slightly) lower SNR.-Arch dude 20:55, 21 April 2007 (UTC)

Thanks, I'll look into a better aeriel, it'll need to be a plug in 'portable' one rather than a roof based one though as the latter isn't suitable for my circumstances. I don't know whether this would be better than an amplifier or not but I'll check them out - what should I be looking for in way of specificaions?. Don't think I'll mess about with beer cans & foil though, sounds like too much hassle. I tried to ask at the avforum h2g2bob linked to but can't access it due to the way my computer's set up. I'll try again from work. AllanHainey 12:25, 22 April 2007 (UTC)

See Yagi array --Tbeatty 06:03, 23 April 2007 (UTC)

Physical terminology

Has anyone ever used the term "inductive coil" to mean "a coil with inductance but no resistance" as opposed to the term "resistive coil"? As far as my knowledge goes, "inductive" doesn't mean "no resistance", but I'd like to hear your opinions. —LestatdeLioncourt 12:39, 21 April 2007 (UTC)

You're going to have to provide context for your question. Are you looking for real devices, or are you trying to win an argument with your physics prof and squeeze an extra mark or two out of your exam?

In practice, it's not uncommon to treat an inductive coil (or some other type of inductor) as having significant inductance and negligible resistance for the purpose of circuit design. It depends greatly on the planned application. Obviously you're very unlikely to encounter an inductor that has absolutely no resistance. TenOfAllTrades(talk) 13:12, 21 April 2007 (UTC)

Agree with above. The term coil usually indicates and inductor with some inbuilt resistance. The term inductor usually implies a peure inductance with no resistance. —The preceding unsigned comment was added by Reincarnation (talk • contribs) 20:54, 21 April 2007 (UTC).

You got it right the second time. The coil in question does have resistance (about 10 Ώ). Is it incorrect to refer to it as an inductive coil, i.e. does the word inductive exclude the existence of resistance? I read a lot outside of our assigned textbook, and I recall coming across such terminology in the sense I'm using it in, but I just want confirmation before I start leafing through thousands of pages. If it were just a point or two, I'd let it go ;) Anyways, if you'd like a "fuller context", let me know. —LestatdeLioncourt 20:26, 21 April 2007 (UTC)

P.S. The prof in question underlined the word "inductor" and put a question mark over it (it was spelled correctly and very clearly). He seems to be unfamiliar with english terminology—nor has he ever used the word himself—which would make sense because he received his education in a wholly different language. So don't just assume that he's automatically right by virtue of his position—he ain't no Shakespeare. —LestatdeLioncourt 20:32, 21 April 2007 (UTC)

No, the word 'inductive' doesn't rule out the existence of resistance. Save for superconducting devices, there will always be at least some electrical resistance associated with an inductive coil. A quality factor, or Q factor, is specified to describe an inductor's performance based on its inductance relative to its internal resistance. (For your own curiosity, it's worth noting that one can simulate a near-ideal inductor using a combination of active components—see gyrator.) Now, whether you need to account for that resistance depends on the specific situation—and on your teacher. Modelling a system with both inductance and internal resistance is somewhat more complicated then a system with either alone.

As far as terminology goes, an "inductive coil" would be a coil designed to have a high inductance for its internal resistance (perhaps wound around a ferrite core, and manufactured out of a high-conductivity material); a "resistive coil" would be made in such a way as to limit its inductance. TenOfAllTrades(talk) 20:50, 21 April 2007 (UTC)

do these issues come under coastal management?

hey guys, my assignment q. is : Discuss the Issues that are present in this coastal environment. i'm doing the derwent estuary in Australia. i just want to make sure if the issues come under 'coastal management'. they are: water quality, wastewater discharges, heavy metals, habitat & species, marine pests, and catchment & flow —The preceding unsigned comment was added by 61.68.2.24 (talk) 12:40, 21 April 2007 (UTC).

Look at the well written Northern Pacific seastar and Derwent River (Tasmania). The pollution used be worse. The interesting effect was to see the unswimmible river flowing past untouched beautiful forest. Dont forget to mention the drought.Polypipe Wrangler 22:58, 21 April 2007 (UTC)

Interesting question about photon energy !

photon are of dual nature(wave and particle) . when the energy of a photon changes by any process(suppose compton effect) ; we say that the wave length of the photon have changed , this explanation stands for wave properties of photon . but photon have particle properties too . what's the change occurs to a photon's particle properties when it's energy changes ?

Take a look at wave–particle duality. According to de Broglie's equation you have a nice changing relationship between wavelength and particle momentum, which has all sorts of nice implications. --24.147.86.187 14:05, 21 April 2007 (UTC)

Shooting star?

Yesterday (Friday 20th April 2007) at about 8:30pm GMT I was looking up at the moon as the sun was setting, and below it to the right was a bright star (I presume it was Venus). Anyway, as I was looking there was a small pin point of light was moving from the north west. It crossed below the moon and Venus and continued on towards the south east. It was traveling quite fast and in a absolutly stright line. It did not look like a pain at hight altutide. What could it have been? A asteroid? There was no tail of light. A saterlight? Maybe. I dont know. Was a saturlight passing over London at 8:30pm? If anyone could tell me what it was please do. Thank you! Think outside the box 12:56, 21 April 2007 (UTC)

Yes, that's along the plane of the ecliptic and about the right time of evening for a satellite, but the problem is it really should have been moving the other way - are you sure the direction you remember is right? I can't tell you what it was specifically, though, without further research... Shimgray | talk | 13:33, 21 April 2007 (UTC)

yes, definitely north west to south east. It was coming from the direction in which the sun was setting. I think it was a saterlight, now that you've told me it was in the right posistion. I didn't know that you could see them from earth. Anyway, thank you, I appreatiate your help. Think outside the box 13:45, 21 April 2007 (UTC)

Ignore that - it is the right direction, possibly. I was misreading - left and right, always confusing!

If you're willing to put a little effort in, you can see the interesting ones :-). If tonight's clear you've a chance of seeing the ISS around nine pm tonight - go to heavens-above.com, give it your location, and ask for predictions. it'll give you a precise time and a star chart to know where to look - and it's a hell of a sight. The actual moving dot isn't much, but being able to see it and know that we did that is really something... Shimgray | talk | 15:06, 21 April 2007 (UTC)

I don't know of any "high altitude pain" that matches your observations, although I do know several "low altitude pains" personally. :-) StuRat 15:40, 21 April 2007 (UTC)

Amateur radio in UK

I'm interested in gettng involved in amateur radio in the uk, but can't find any reliable information on how to get started. I know about licenses and the like, and have enough experience and knowledge on non-amateur radio nets (in terms of voice procedure and theory) to pass the foundatin license. What I'm wondering in what sort of kit I need to buy to get started, and if there are any good UK focused sites out there with info. —The preceding unsigned comment was added by 81.159.227.103 (talk) 14:21, 21 April 2007 (UTC).

Try looking at Radio Communication magazine or Practical Wireless if its still going. Other wise why not build your own- thats what Ham radio used to be about

Building your own is cool, and probably something you'd want to do at some point. However, if you aren't already familiar with electronics design, I would rather recommend buying a kit, consisting of components and assembly instructions. You get to put it together yourself, which is fun, and you need not know much else than how to solder. (I don't know of any specific kits, though.) —Bromskloss 18:20, 21 April 2007 (UTC)

You need to visit http://www.rsgb.org/ G N Frykman 06:17, 22 April 2007 (UTC) (G0GNF)

Learn Morse. Some licenses may not require you learn it, but it's useful if you want to get serious. Learn about the radio spectrum, how it is used, and where the amateur bands are. Learn where your interests lie -- morse over HF, connect with other amateur enthusiasts around the world, etc., or shorter-range voice over VHF, etc. Learn some basic electronics. Learn about propagation theory. That ought to get you started, at least? —The preceding unsigned comment was added by 149.135.97.83 (talk) 12:09, 22 April 2007 (UTC).

snake repellant

144.134.109.178 17:26, 21 April 2007 (UTC)Is there any known repellant for snakes, either chemical or organic.

Apparently there is. Naphthalene interferes with the vomeronasal organ of snakes, thereby disrupting their olfactory system in a reversible manner. Apparently they don't like this and tend to make an escape from the source of the naphthalene. Products such as Snake-A-Way use this. The effectiveness of such products are under debate, though. The University of Florida demonstrated that "Snake-A-Way repels the poisonous coral snake and six species of rattlesnakes with 'remarkable effectiveness,' but is somewhat limited in controlling other snakes such as cottonmouth." [1] However, the University of Nebraska reported that similar "substances tested did not elicit avoidance behavior in the plains garter snake" and suggested "usage of these repellents should be discouraged." [2] There is an alterntaive product called Bonide Snake Stopper, that contains clove and cinnamon oils. Which, apparently, "federal research has found to repel snakes." [3] Rockpocket 19:07, 21 April 2007 (UTC)

I've found them to be quite allergic to lead, at least when it's administered with a double-barrel shotgun. :-) StuRat 21:38, 21 April 2007 (UTC)

Done the 12gauge& 410 thing , lotsa snakes in the NT , ammo running low, tell my wife to get the long handle shovel back out. Thanks for the help, I'll give it a go.

Guard dog question

I'd like to breed the most vicious and powerfull canine beast possible and was wondering what the most effective way to do that is? I was thinking of crossing a hyena with a great dane, wolf, pit bull and German shepard. Are there any breeding tricks to encourage giaganticism and unstable and psychotic behavior? Food isn't a problem, I raise cattle here at the coumpound. Thanks. PatriotSurvivor 23:01, 21 April 2007 (UTC)

You could interbreed all of those except the hyena, that's an entirely different species. I should also point out that the last thing you want is a dog with psychotic behavior. Such a dog is more likely to attack you than any would-be attacker. StuRat 23:45, 21 April 2007 (UTC)

I don't want to be presumptious but you really seem to have far less than the minimal knowledge about both animal behavior and basic genetics that would be necessary to breed animals successfully. Why don't you just go with one of the breeds of dogs which have already been bred for generations to be violent? --24.147.86.187 01:14, 22 April 2007 (UTC)

By the way, we won't be able to help you with the legal and medical issues arising from any mayhem your beast may cause. Clarityfiend 01:36, 22 April 2007 (UTC)

How many family member's do you have? Just wondering because I don't want the beast to starve when it's done eating you and your cattle Nil Einne 22:25, 23 April 2007 (UTC)

Creating a horrible beast requires but one thing: you mistreat it horribly. Getting a bigger dog will obviously raise its potential for destruction, but a little pitbull latched onto an interloper's hand can cause terrible damage too.

Hyenas are very intelligent and head-strong: good luck subordinating anything with hyena parentage to your will. Vranak

Hyenas are more related to cats than they are dogs, actually. Although if you had the money, you could possibly do some gene splicing. bibliomaniac15 05:22, 22 April 2007 (UTC)

Hmmm ... with regard to training and treatment, it might be prudent to check your local animal cruelty legislation - if you live in the USA, there are links here. Generally speaking, it is usually an offense to torture or starve animals or cause them to fight one another. Gandalf61 09:52, 22 April 2007 (UTC)

Sorry to be so cynical, but it's only illegal if you get caught. Vranak

does it have to be a dog. You could use a wild animal to guard whatever it is, such as a wolf or a tiger.

Ha! That would not work. You can't have an animal with dignity working as a slave. Vranak

Well, if you want to make your dog is large, you should make sure it has specific alleles of its insulin-like growth factor 1 gene. [4] Rockpocket 18:45, 22 April 2007 (UTC)

Thank you all for the good answeres. I never knew that hyenas were cats (kinda)! To Vranak, I hadn't thought of abusing the animal to make it more vicious - what a horrible thought. Unfortunately there are people in this world that would do that. I'd much rather have a happy and well cared for guard dog, but naturally aggressive. PatriotSurvivor 22:38, 22 April 2007 (UTC)