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August 16

Common/Household "soft" magnets

What are some "soft" magnets that you can find in your household? —Preceding unsigned comment added by 71.52.198.240 (talk) 00:23, 16 August 2008 (UTC)[reply]

Soft vs. hard means the mobility of the magnetic domains inside the material. Iron is a soft magnet, since its domains will align with whatever magnetic field it is in. Mac Davis (talk) 03:15, 16 August 2008 (UTC)[reply]

I am told tht ordinary nails are made of iron (soft ferromagnetic material). If you magnetize a nail, it easily loses its magnetism when the current in the coil surrounding it is turned off, or it you tap it sharply. Most common ferrous household objects are steel (hard ferromagnetic material), such as appliance casings, hinges, shelf standards, beams and angles, and even sewing needles. In transformers, the cores are soft ferromagnetic matrial. Relays would have soft ferromagnetic cores as well, as would doorbell or solenoid cores, so that they lose their magnetism when the current is turned off. The nature of a ferromagnetic material could be analyzed by measuring the hysteresis curve and seeing how much magnetism is retained. Edison (talk) 05:00, 17 August 2008 (UTC)[reply]

Don't forget speakers; the electromagnet inside has to change its properties very quickly for the device to produce any usable sound. --Bowlhover (talk) 09:50, 17 August 2008 (UTC)[reply]

In modern speakers I have seen a permanent magnet and a coil of copper wire attacked to the voice coil. Where is the soft ferromagnetic material?Edison (talk) 14:56, 17 August 2008 (UTC)[reply]

Vitamins

Is Vitamin short for Vital Minerals? Or is it something else. --69.152.197.134 (talk) 04:06, 16 August 2008 (UTC)[reply]

It's derived from the Latin "vita", meaning "life", and from the Latin "amine". Scientists at the time believed vitamins were amines; when this was shown to be false, the "e" was dropped. See [1]. --Bowlhover (talk) 04:37, 16 August 2008 (UTC)[reply]

Or of course you could read Vitamin. --Heron (talk) 09:37, 16 August 2008 (UTC)[reply]

food science

Why does liver of meat especially of chicken turns green while cooking? What's the name of the pigment in shrimps responsible for changing into red while cooked? —Preceding unsigned comment added by Gnanesh123 (talk • contribs) 06:11, 16 August 2008 (UTC)[reply]

To the second question, astaxanthin. See [2] and [3]. --Bowlhover (talk) 07:18, 16 August 2008 (UTC)[reply]

IUPAC Nomenclature of carbohydrates

What do the letters R and S stand for in the IUPAC nomenclature of carbohydrates?(e.g., fructose is (2R,3S,4R,5R)-2,5-Bis(hydroxymethyl)oxolane-2,3,4-triol)Leif edling (talk) 08:09, 16 August 2008 (UTC)[reply]

I don't really have a clue, but my guess would be the chirality. -- Aeluwas (talk) 09:39, 16 August 2008 (UTC)[reply]

Yes, it describes the chirality. In organic compounds such as carbohydrates, wherever there is a carbon atom that has four different groups attached to it, there are two possible arrangements of those four groups. Each is a mirror image of the other, and one is designated as R and one as S. -- Ed (Edgar181) 16:12, 16 August 2008 (UTC)[reply]

As for what the R and S are abbreviations of, it is Rectus and Sinister, the latin words for right and left, respectively. (See Chirality (chemistry)#By configuration: R- and S-) -- 128.104.112.147 (talk) 21:19, 16 August 2008 (UTC)[reply]

Obtaining special dc power supply.

i need to obtain special dc power supply for a project. the power supply system will supply varying power with respect to time.

File:Dc power supply for project.jpg

the horizontal axis indicates time. how this type of power supply system can be constructed? where in the web i can obtain a circuit diagram for this power supply system? —Preceding unsigned comment added by Shamiul (talk • contribs) 09:28, 16 August 2008 (UTC)[reply]

You don't indicate any units on your graph, so we can only guess at the voltage (or other electrical parameter) and frequency that you want. One well-known circuit that produces this waveform is the flyback circuit for a CRT. There are many circuits [4] for this on the web. [Safety information: the flyback circuit can generate tens of thousands of volts, so don't use it unless you know what you're doing. For smaller voltages, use the humble 555 timer IC. Its data sheet will tell you how to get a triangle wave out of it.] --Heron (talk) 09:35, 16 August 2008 (UTC)[reply]

theres programmable psus you could buy to do this. One I remember was a BOP (bipolar operation power supply) make by Kepko. However if its only a fixed application you need, you could build your own by using a ramp generator followed by a power output stage. —Preceding unsigned comment added by 79.76.213.193 (talk) 12:04, 16 August 2008 (UTC)[reply]

It should be pointed out that what you are looking for is an AC supply - not DC. If you Google "Ramp generator" - you'll find a ton of circuits you can build to make the waveform you seek. You can also search on "Signal generator" to find a bunch of pre-packaged systems that generate these kinds of waveforms - although typically not at high voltages or current. But without knowing specifics of current, voltage and frequency that you need to supply - it's impossible to recommend a specific product.

Actually the Op was correct: hes looking for a direct current supply. It may not be steady, but its direct. —Preceding unsigned comment added by 79.76.158.77 (talk) 01:35, 17 August 2008 (UTC)[reply]

Some power supplies are "programmable" in the sense that you can feed them an analog voltage (at a very low power level) and the power supply will output a voltage that is proportional to the "programming" voltage. If the frequency of your waveform is low (less than, perhaps ten Hertz), such a power supply could be used with any number of simple waveform-generation circuits to produce your desired effect. (See function generator.) Alternatively, consider an emitter follower connected between an ordinary constant voltage power supply and your load, with the 'follower being driven by a waveform generator. (Also, if your power requirements are small enough, you might find that a function generator itself can output the power directly.) You can also buy "bipolar power amplifiers" that can help here, but they tend to be pricey.

Atlant (talk) 18:02, 19 August 2008 (UTC)[reply]

Evaporating black hole

What stays back when a black hole evaporates? The formulas on Hawking radiation don't seem to apply to very lightweight black holes. The evaporation is done by absorption of one partner of pairs of virtual particles but does this still work when they become really small, say, smaller than the wavelength of a photon corresponding to the mass (energy) of the black hole itself? And how often do virtual particles pop up from vacuum? 93.132.173.139 (talk) 12:39, 16 August 2008 (UTC)[reply]

I'm not entirely sure I understand what you are asking, but I think when a black hole evaporates, it just evaporates into electro-magnetic radiation, so nothing is left behind when it evaporates completely. ScienceApe (talk) 20:59, 16 August 2008 (UTC)[reply]

Well, it's difficult to ask the question precisely. What I have in mind is this: as long as the black hole is big enough to catch virtual particles, the formulas about Hawking radiation apply. But when the BH is really small I imagine it becomes more and more difficult to catch virtual particles. That opens a lot of questions about virtual particles and photons in general: what size is a photon, can it be absorbed by a structure that is far smaller than its wavelength? At which probability? If this is not possible at all, something stable will remain. If this is possible, the rate of evaporation will not be the same as for larger BHs. And what if the BH swallows a virtual photon with twice it's energy? Would we have a black hole with negative mass? 93.132.189.68 (talk) 08:06, 17 August 2008 (UTC)[reply]

It may not be a good idea to think of the evaporation in terms of virtual particles. Hawking does mention the virtual particle picture in his 1975 paper, but he says it's "heuristic only and should not be taken too literally". His actual derivation of the effect ("The real justification of the thermal emission") uses nonperturbative field theory, which doesn't have the virtual particle concept. You can describe any particle decay in terms of virtual particles if you want to. For example, instead of saying that a muon decays into an electron and two neutrinos, you can say that an electron-positron pair appears out of the vacuum, the positron interacts with the muon producing two neutrinos, and the electron escapes without interacting and "becomes real". Since the electron carries energy and overall energy is conserved, the positron must have carried negative energy to the muon. So there are "enough" virtual particles in the vacuum to cause the decay of even a pointlike particle like the muon, and presumably there would be enough for a tiny black hole as well. But nobody really knows for sure, since the combination of classical general relativity and quantum field theory that Hawking used breaks down for very small black holes, and we still don't have anything better. People believe that black holes decay completely simply because every quantum object decays unless there's a conservation law preventing it, and no known conservation law would prevent the decay of black holes. (Hawking also mentions this argument in his paper.) I've heard it suggested that black holes don't decay completely but leave a "Planck scale remnant" behind, but this seems to be based not on the plausibility of a "Planck scale remnant" but on the fact that it would solve the black hole information loss problem. -- BenRG (talk) 12:06, 17 August 2008 (UTC)[reply]

Thank you for the link, that looks the right stuff but not the kind to be understood in a minute. 93.132.189.68 (talk) 16:27, 17 August 2008 (UTC)[reply]

Calcium and Acne

I notice that after taking calcium supplements, my acne gets reduced and I have heard similar claims from other people. What role does calcium play in reducing inflammation or is there a different mechanism? Or is this just a placebo effect? 96.242.14.160 (talk) 13:28, 16 August 2008 (UTC)[reply]

It could only be placebo if you believed in advance that calcium would do that. Is that true? If not - no placebo. SteveBaker (talk) 13:56, 16 August 2008 (UTC)][reply]

It's not necessarily a placebo, but it's certainly an unreliable conclusion if you believed calcium would reduce your acne before you started the therapy. That's why most trials for drugs are blind. However, there is some evidence that calcium aids the body's endocrine systems and is occasionally used as a treatment for acne. See PMID 17576242. —Cyclonenim^T@lk? 14:24, 16 August 2008 (UTC)[reply]

Glucose question

under what conditions does a patient needs to be in drip of glucose. —Preceding unsigned comment added by 121.245.25.17 (talk) 14:54, 16 August 2008 (UTC)[reply]

I fixed your question to a new section. Acute hypoglycemia can usually be reversed with an oral dose of 10-20g of carbohydrates. However, when EMTs find someone in a state of severe hypoglycemia, they usually administer an IV drip. —Cyclonenim^T@lk? 15:01, 16 August 2008 (UTC)[reply]

Hospitalized patients are often kept on IV fluids containing dextrose (glucose) in order to maintain both hydration and caloric intake for short periods of time. This might happen in a number of situations: 1) they are ordered not to take anything by mouth in advance of a procedure, 2) they are undergoing or recovering from an operation, or 3) they are unable to take in fluids or nutrition due to their medical condition. Total parenteral nutrition (TPN) is a mixture of dextrose, amino acids, and lipids that is used to maintain a more complete nutritional status over longer periods of time. An individual with an inborn error of metabolism who is hospitalized for an acute episode of metabolic decompensation may be maintained on a higher concentration of IV glucose to prevent a catabolic state, as this can worsen the metabolic condition. Medical geneticist (talk) 17:01, 17 August 2008 (UTC)[reply]

Adding to the above, if someone has taken an overdose of a long-acting hypoglycemic agent (either oral or insulin), though they can be revived temporarily with oral glucose, a drip will be required to keep their glucose levels normal until the agent wears off. - Nunh-huh 01:31, 18 August 2008 (UTC)[reply]

(edit conflict w/Cyclonenim) Most of the time when people use the term EMT they mean EMT-B. In many jurisdictions, EMTs are not permitted to perform invasive procedures such as IV therapy until they upgrade their training to EMT-I (AKA CRT) or EMT-P (AKA Paramedic). EMTs can only give oral glucose, usually as a paste (which tastes gross) but often use other available sources such as juice or cake frosting. --Shaggorama (talk) 02:58, 20 August 2008 (UTC)[reply]

type I diabetics are sometimes first diagnosed in a state of ketoacidosis, and in such cases they are administered insulin and glucose drips simultaneously until the ketoacidosis clears and their blood-sugars stabalize. (See Diabetic ketoacidosis#Treatment) Oded (talk) 03:35, 20 August 2008 (UTC)[reply]

Electronically squaring a signal

This is for a home project/ personal interest. Can a unipolar signal be squared (ie multiplied by itself) by first taking the natural logarithm (using a log amp), multiplying by 2 then taking the anti log using an exponentiating circuit? And what would happen if the multiplier were not 2: could you get odd powers of the input signal. Would the odd powers introduce other frequency components in the output? —Preceding unsigned comment added by 79.76.158.77 (talk) 16:30, 16 August 2008 (UTC)[reply]

Yes, yes, and yes. Some analog computers work using logarithms. In fact Zetex released an IC a few years ago [5] that used the same principle. Raising a signal to a power is a nonlinear operation, so you would necessarily generate harmonics. --Heron (talk)

OK thats good thanks- but, would it be easier and/or better to use an analog multiplier for pure squaring rather than a log amp: I mean would the multiplier be faster than a log amp? (I have a time domain signal-- pulses)--79.76.158.77 (talk) 00:42, 17 August 2008 (UTC)[reply]

Just a niggle, but isn't a unipolar signal just 0 or 1? If it really were a unipolar signal all you have to do to square it is pass it on unchanged. Dmcq (talk) 21:52, 16 August 2008 (UTC)[reply]

No, that's a binary signal. Unipolar means it stays on one side of 0 V. --Heron (talk) 22:05, 16 August 2008 (UTC)[reply]

Is everything technically light?

I'm aware that our eyes can only see only a paltry slice of the electomagnetic spectrum. What's interesting to me, however, is how special equipment can take just about any wave and "interpret" it for our vision (such as untraviolet, thermal radiation,etc.).I vaguely remember reading somewhere this can even be done for sound! Apparantly some animals and insects can "see" wavelengths that we can only measure. So is all existence merely wavelengths of light? What profound lesson (if any) can be drawn from this?--Hey, I'm Just Curious (talk) 17:10, 16 August 2008 (UTC)[reply]

No, light is distinct from matter. Our eyes can only see the visible light spectrum. However, the other wavelengths of the electromagnetic spectrum are still there, it's just our eyes can't detect them. Infrared and ultraviolet light can be picked up by sensitive equipment which converts it into forms of visible light. It is not because everything around us is made from light. You may wish to see Thermographic camera for infrared and Ultraviolet photography. —Cyclonenim^T@lk? 17:34, 16 August 2008 (UTC)[reply]

In some broader sense the OP is right. Very much of what happens in everyday life is either due to gravitation or to electromagnetic forces. If you put your coffee mug on your table an it doesn't sink in, that is because the electromagnetic force exchanges photons (light) between the two. 93.132.173.139 (talk) 18:09, 16 August 2008 (UTC)[reply]

I don't think that was the OP's point, though. I think they were suggesting that matter and light are the same thing which isn't true. Unless we start going into wave-particle duality. —Cyclonenim^T@lk? 18:31, 16 August 2008 (UTC)[reply]

Light is a very specific form of electromagnetism. The force holding atoms apart is the same fundamental force, but I don't think it's really accurate to called it "light". --Tango (talk) 18:43, 16 August 2008 (UTC)[reply]

Light is different from other stuff. For instance, you can't capture light (or sound) inside a bottle and unless you have a multi-billion dollar lab, you can't make two particles of light collide and bounce off each other. This is a trick that most other stuff, like doors and foreheads, easily manage.

Electromagnetic waves of "Light" with different wavelengths than visible light can also behave so different from ordinary light that you may not have recognized it as light, could you see it. While visible light travel mostly in a straight line, radiowaves can curve around mountains like waves around a dock in a harbour and it would be more difficult to see anything but the biggest features of the landscape around you. So while quantum mechanics allow us to say that everything is both waves and particles, we can't say that everything is "light".EverGreg (talk) 15:33, 17 August 2008 (UTC)[reply]

Everything may appear to be light through an infrared camera, but this is just because most things emit infrared radiation, commonly known as heat. Only an object at Absolute Zero would not theoretically emit infrared radiation, and a normal infrared camera would display this object as completely black. RevenDS (talk) 21:17, 21 August 2008 (UTC)[reply]

"Most chemicals are white."

This statement appeared earlier on this page in a discussion titled The End of the World. Is it true that most chemicals are white? If so, why?

Thanks, Wanderer57 (talk) 17:57, 16 August 2008 (UTC)[reply]

Because they rarely have a chromophore? --Ayacop (talk) 18:28, 16 August 2008 (UTC)[reply]

Continuing on, yes, unless there's a chromophore, it's actually colorless. Even my college chemistry students have a difficult time distinguishing between "color" and "transparency" (a white thing is colorless+opaque, not a "color" itself). Suspensions (as opposed to solutions) are non-transparent (tindall effect) and collections of small particles (as opposed to solid crystals) are often cloudy or opaque. Both of these are due to seeing reflections and refractions from the surfaces and edges of the pieces, not due to the chemicals of the materials themselves. So the common form of a colorless thing may often be white. Look carefully & closely at a single grain of salt, then look at a shaker-full of them.

The link above should be to Tyndall effect. Dostioffski (talk) 21:07, 16 August 2008 (UTC)[reply]

Thank you. I would like to restate my question taking into account the above discussion re transparency. Is it true that in crystalline form most chemicals are colorless? Is it true that in powder form most chemicals appear white?

I am puzzled as to why the topic was changed from the "chemistry of color" to the innate significance of colors. Quite a jump. Wanderer57 (talk) 18:40, 17 August 2008 (UTC)[reply]

Above comment copied without modification from below after I added a subject heading Nil Einne (talk) 19:04, 17 August 2008 (UTC)[reply]

The colour white

Added subject heading to what is basically a different question to avoid either question being lostNil Einne (talk) 19:00, 17 August 2008 (UTC)[reply]

What is there about the color white that gives it a special status in the minds of human beings? Some societies give some other colors a special significance, but this is consciously (or politically) assigned. rather than being innate in the human mind as white seems to be. White is a mixture of other colors in certain proportions. If the proportions of the mixture are changed, a color other than white will be obtained that will not have an innate status. Andme2 (talk) 02:19, 17 August 2008 (UTC)[reply]

If anything, I would argue that black may have innate significance, since humans tend to have an innate fear of darkness (due to the significant disadvantage it puts us at because we rely so much on our visual system). The contrast to this state is "whiteness", the impression of any combination of colors of light that equally stimulates all three types of color-sensitive visual receptors. That is more of a light/dark issue than one of specific colour, though it may explain the special status our cultures tend to give black/white over other colours. Dostioffski (talk) 04:56, 17 August 2008 (UTC)[reply]

Does white really have a special/inate status in the minds of humans? What evidence do you have for that? It definitely doesn't universal cultural significance. For example, white denotes purity and innocence in Western cultures but is associated with death and mourning in East Asian cultures. In South Asian cultures, it's associated with both... Red given the high contrast, similarity to blood and other factors also tends to have special status in many cultures. Nil Einne (talk) 15:16, 17 August 2008 (UTC)[reply]

Thank you. I would like to restate my question taking into account the above discussion re transparency. Is it true that in crystalline form most chemicals are colorless? Is it true that in powder form most chemicals appear white?

I am puzzled as to why the topic was changed from the "chemistry of color" to the innate significance of colors. Quite a jump. Wanderer57 (talk) 18:40, 17 August 2008 (UTC)[reply]

Don't ask me, ask andme. However since they are indeed seperate questions to avoid either question being lost, I've added a subject header to AndMe's question Nil Einne (talk) 19:00, 17 August 2008 (UTC)[reply]

Agreed. I should have started a new subject. Yes, white is given a different significance in different societies. But my point is that white has an innate, though indeterminate, significance. Red, also, seems to have an innate significance but less intensely so than white, and red also can be assigned an arbitrary association. Furthermore, the shade of red is less important. It can be pure red (one wavelength in the light spectrum), or a shade of red (that includes other colors). There is only one white color - it is always a certain mixture of colors in certain proportions. Off-white does not have an innate significance. In fact, off-white may be regarded with contempt as dirty white - something masquerading as the color that has real innate significance. I don't think anyone would refer to a shade of red as dirty red - it would probably be called dark red. Andme2 (talk) 07:53, 19 August 2008 (UTC)[reply]

Do you have any real evidence that all cultures,( particularly those who have little contact with the 'outside' world) hold white to be significant? And that all cultures consider offwhite as "dirty white"? Also, I would say there isn't actually just one white. For example, adding blue makes white seem whiter. But most people would still agree that not so blue white is white. There is a difference in white balance preference with monitors etc depending on culture (also with lighting). And pink is probably not red in most cultures. And I don't personally believe, nor have I seen any evidence that the significance of red is more or less inate then white. Nil Einne (talk) 11:24, 19 August 2008 (UTC)[reply]

The OP may be interested in Basic Color Terms: Their Universality and Evolution by Berlin and Kay. Our article is pretty short but gets the basic point across. If their theory is correct, black and white are both innately and universally significant, with red coming next, but somewhat lower. Matt Deres (talk) 20:19, 20 August 2008 (UTC)[reply]

I was glad to see in the last post that organized research has found that white, black, and to a lesser degree red, have an innate (though basically indeterminate) significance to humans. This corroborates my own thinking on the matter. I was not aware that research had been conducted on this, with scientific papers and at least one book.

Having that corroboration, I will go one step further – a step which I thought would be too "off-the-cuff" to be posted. (An anonymous poster has chided me because I did not refer to scientific papers. In fact, he told me to "shut up".)

First, we must bear in mind the distinction between spectrally-pure (sine-wave) color and complex color (which combines sine waves of differing wavelengths, thus forming a non-sine wave). Also, living things vary in their physiological and psychological response to colors. Some humans are partially or completely color blind. Women are said to prefer red and orange; men prefer green and blue. Cats, apparently, have sacrificed some color awareness to an ability to see in faint light. Some insects see ultra-violet (I wonder what it looks like to them).

From a human standpoint, I think white has only one shade that can truly be called "white". One poster has said that blue-white has an even greater psychological significance than white. Another poster said different societies have slightly different concepts of what "white" looked like. I don't know what to say to these thoughtful remarks, so I will proceed with the idea that there is only one white to the human conscious, not blue-white and with no other shades.

Red, though secondary in innate significance, has a great many shades. The shades may be given names other than "red" (such as "maroon" or "crimson"). But to the human mind all shades of red have an innate significance not shared by colors that are basically not red.

Lipstick (almost always red) comes in an amazing range of shades. A large drugstore will show a very large variety of lipstick shades in chart form in their cosmetics department. Sometimes I walk out of my way in a drugstore just to see the great display of red shades. (I am a normal male.)

As I mentioned, some shades of red have been given a name (such as "maroon" or "crimson"). These shade-words (for all colors) could be added to the 11 basic color-words in the English language that have been posited by Berlin and Kay. According to their theory, I think, the total number of color and shade words would indicate the degree of civilized advance of a society.

Many shades of red have not been given a name (except for fanciful, promotional names given by cosmetics manufacturers!)

(To be continued in my next post in this thread.) Andme2 (talk) 08:17, 22 August 2008 (UTC)[reply]

Here is my far-out, off-the-cuff, idea. Perhaps each shade of red has a unique message. It is not a message that can be put in words. It is also basically indeterminate, at least within a broad range.

Each musical composition, too, has a unique message. The message of music is expressed only vaguely (if at all) by the title or the words (if it has words). The music itself is the real message. Music has been referred to as a universal language. It is understood by people who have a knowledge only of different languages. (Though some societies do not understand the music of other societies.) Music is entirely separate from the socially-assigned meaning of sound-groupings (words) made by the human mouth and vocal cords.

As with music, so it is, perhaps, with shades of red. Each shade of red has a unique message. It is separate from any arbitrarily-assigned political or social significance. Shades of red are also permanent in their meaning. (Red had an indeterminate meaning long before it was associated with communism.) Each shade of red conveys a single meaning, unlike music in which notes are presented in sequence to convey a complex message. Presenting colors in sequence would not do anything, though juxtaposing different colors in a great painting has a significance much greater than the individual colors. Abstract painting, if good, would be one way to do it. (To be continued in my next post in this thread.) Andme2 (talk) 08:17, 22 August 2008 (UTC)[reply]

Perhaps colors other than white, red, and black also convey a message. (Black, strictly speaking, is the absence of color.) The message of these other colors is not as intense as white, black and red, but there is a message. When I am in a hardware store, I enjoy looking at the amazing range of colors in the paint color-sample charts. What are they all saying? It cannot be put into words, just as the meaning of music cannot be put into words. Andme2 (talk) 08:17, 22 August 2008 (UTC)[reply]

While you are obviously welcome to your opinion, you may want to read white, colour temperature [6], [7], [8] (look for Asia) &

Bluing (fabric) and consider how this correlates with your idea there is only one white. In particular, you may want to considr the difference between a blueish white and a yellow/red white and where precisely in the colour temperature scale is the 'true' white that you believe exists and also, how this fits in with the idea that colour temperature preference varies between cultures and whether all cultures will agree with your notion that whatever colour temperature you feel is the true white is indeed the true white or they may find another colour temperature more 'whiter' then you white (or several colour temperatures equally white). P.S. I came across [9] which appears to address your ideas more generally and does seem to support the idea, at least among the study groups, that white has special significance (although not the only colour with special signifance). P.S. Incidentally, those colour temperature preference ranges are for lighting, I'm pretty sure monitor colour temperature ranges are rather different although again I believe there is varience between person and this is at least part culturally bound. Nil Einne (talk) 12:28, 23 August 2008 (UTC)[reply]

Electromagnet, Again

What would be the force of newtons with two electromagnets; each magnet having 1.2 volts, with an iron core, and 70 wraps of copper wire? —Preceding unsigned comment added by Hovercraft Experts (talk • contribs) 21:23, 16 August 2008 (UTC)[reply]

Again, use the equations on the electromagnet page. You'll learn a lot more about this project if you are able to do things yourself rather than asking someone else to use a calculator for you. BTW, you still didn't provide enough information. DMacks (talk) 21:43, 16 August 2008 (UTC)[reply]

Much better information, but you need to know the amperes which flow through the 70 wraps, which depends on the resistance. This could be calculated from the gauge and length of wire. Then the physical geometry of the iron cores (bar or horseshoe shape? What cross section area?) and the distance between will have a huge effect. The information given would not allow a calculation even within an order of magnitude. Note that if 1.2 volts is the voltage with no current flowing, the actual voltage in operation will probably drop significantly with only 70 turns of wire, which is close to a short circuit. Edison (talk) 04:52, 17 August 2008 (UTC)[reply]

Also note that the direction the currents flow in determine the sign of the force. If the current flows clockwise as viewed from one end, that end is the south pole, and vice versa for a current travelling counterclockwise. Like poles attract, so electromagnets with electrons flowing in the same direction attract; they repel otherwise.

Another crucial factor is the number of turns of wire per unit length of iron core. Wrapping 70 5-cm-thick cables around a core is obviously going to produce a weaker magnetic field than using 70 0.1-mm-thick wires if the current doesn't change.

To calculate current, use Ohm's law, the resistivity of copper (approx. 17 nanohm-metres), and the electrical resistance formula. --Bowlhover (talk) 10:50, 17 August 2008 (UTC)[reply]

If the conductors are 5 cm thick or 1 mm thick, and carried the same amperes through the same number of turns, and were along the same lengh and cross section of core, I would expect the same magnetic field strength. The 1 mm conductors could be spaced apart, or the 5 cm conductors could be applied in multiple layers. Edison (talk) 14:54, 17 August 2008 (UTC)[reply]

That's true--it's the number of turns per unit length of core that affects the current. --Bowlhover (talk) 19:21, 17 August 2008 (UTC)[reply]