Wikipedia:Reference desk/Archives/Science/2007 May 1

From Wikipedia, the free encyclopedia

< Wikipedia:Reference desk | Archives | Science

Science desk
< April 30	<< Apr \| May \| Jun >>	May 2 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

[edit] May 1

[edit] Top Ten parasites

Ive looked every were and havent found any thing im trying to find. I some way to identafy the top ten worst parasites. Every were i go nothing tells me anything ive tried Google ask jeeves but nothing so i hope u can help me.

70.133.64.95 00:52, 1 May 2007 (UTC)Tony

How do you define "worst"? -- mattb 00:54, 1 May 2007 (UTC)

Make your choice from Category:Parasites. However, if you wish to know which parasites have the greatest impact on human mortality and morbidity, this page might help. Rockpocket 01:09, 1 May 2007 (UTC)

For simply bizarre and horrific parasites, see this page. --Joelmills 01:17, 1 May 2007 (UTC)

I've always been partial to dracunculiasis and the dread loa loa worm, but on television recently it seems the more popular alternative is the penis worm. - Nunh-huh 01:57, 1 May 2007 (UTC)

The family of parasites that cause African sleeping sickness and chagas are pretty nasty when you consider that they cross the blood-brain barrier. - AMP'd 01:56, 1 May 2007 (UTC)

Candirú should have an honored position on such a list. --TotoBaggins 02:02, 1 May 2007 (UTC)

If your intrested in animals like this you should check out animal planet or National geographic chanel they have little specials on animals like this =) you might get lucky and catch one sooner or later. User:Maverick423 If It Looks Good Nuke It 15:13, 1 May 2007 (UTC)

[edit] E. Coli

Escherichia coli does not seem to mention how the bacteria get in to a human. Billions or trillions of E. coli cells live in an average human. I imagine that a newborn baby does not have such bacteria inside; by what age is it fair to say "most" humans have a healthy population of E. Coli? If it is pres<link rel="stylesheet" type="text/css" href="http://en.wikipedia.org/w/index.php?title=User:MarkS/XEB/live.css&action=raw&ctype=text/css&dontcountme=s">ent since birth, is it really fair to call the E. Coli a separate organism from the human host? Nimur 01:46, 1 May 2007 (UTC)

In fact, E. Coli make up only about 1% of the intestinal flora of adult humans, but is one of the predominant members of the flora of the intestines of infants (along with lactobacilli and enterococci). The E. Coli, like all other commensal flora of the gut, enters the gut when it is ingested. And, yes, of course E. Coli and humans are separate organisms. - Nunh-huh 01:54, 1 May 2007 (UTC)

To elaborate a bit on Nunh-huh's last comment. E.coli is a seperate organism because it is happy to live by itself outside the human body. It is not dependent on us for its replication, it has its own DNA and will happily grow any place where the conditions meet it's standards (which aren't very high btw). E.coli just finds our colon a very nice place to hang out. We give it nutrients, warmth and moisture and in exchange E.coli gives us vitamin K. PvT 13:40, 1 May 2007 (UTC)

E. coli will get into the human via the mouth. Because there are so many of these bacteria around, every time we eat we will be consuming some E. coli along with the food. It is hard to keep a baby completely sterile. At some point the cells evade digestion in the stomach and make it to the intestine where they grow. GB 00:44, 2 May 2007 (UTC)

IN response to the previous statement, there is no reason why you would ever try to keep a baby sterile. Human's harbour symbiotic bacteria for a reason, and where they are not present you become vulnerable to infections. A simple example is proliferation of candida albicans (thrush) when a woman takes certain antibiotics. Although E. Coli can be dangerous and one of the main causes of food poisoning and STIs, it is not harmful whilst in the colon. It is the same case with all comensal bacteria. As long as they stay in the right place, you are fine. They can only become harmful if you are immune impaired for some reason or if they migrate.80.6.120.85 11:51, 2 May 2007 (UTC)

Not all E.Coli are the same - there different strains and certainly Escherichia coli O157:H7 is never comsensal but causes illness and with various toxins causing life threatening illness. Other (ie non-O157:H7) are harmless and normal to have. David Ruben ^Talk 23:36, 2 May 2007 (UTC)

[edit] Edde triggered logic

Any idea how can edge triggered logic be implemented behaviorally??59.92.241.28

Not sure what you're after, but have you read flip-flop? -- mattb 12:58, 1 May 2007 (UTC)

I don't think there actually exists such a device as an "edge-triggered latch"; we just use that term as a sort of short-hand because it's an approximately-correct description of the observed external behaviour. Internally, I think all edge-triggered devices are really more like "transparent latches" that are "opened" by a pulse derived from the clock passing through a delay stage. That is, the delay stage sets the amount of time that the transparent latch is open, and for most purposes, it's an infinitesimal period of time that roughly corresponds to just the edge of the clock pulse.

If you look in the old TI 54/74 series TTL handbook, you'll find detailed diagrams for most of the common flip-flop families.

Atlant 13:13, 1 May 2007 (UTC)

[edit] CRT Tube

Any idea what picture characteristics should degrade and in what amount in a CRT tube??Well my comp monitor is about 5years old with about 4000hrs usage, and the sides seem a slight blur(out of focus).Is this normal or can it be corrected?59.92.241.28

You can usually cure that blurring by degaussing the CRT. the internal degaussers (if any) may be insufficient to completely degauss the CRT. The main age item for a color CRT is the phoshpors. The colors tend to go off.This is noticable when you have CRTs of various ages in the same location. Of course, you can "burn" an image into a location on the screen if that image remains fairly constant for weeks at a time.The originaljustification for "screensavers" was to avoid this effect.I do not know if modern CRTs still suffer from this. -Arch dude 02:22, 1 May 2007 (UTC)

That sounds like it could use some degaussing - but modern monitors do that automatically every time you turn them on. Perhaps if your has a 'Menu' or 'Settings' button on the front, you could try looking through the menu system to see if there is a 'Degauss' option. If you find it, the monitor should emit a loud click - then the screen will shimmer a bit - and maybe - if you have lead a blame-free and moral existance - the monitor will sharpen up a bit. Sometimes you have to do it several times. But that might not be it. If the 'blur' is actually colour alignment (if you put a white dot in that blurry area of the screen, do you see three overlapping red/green/blue dots?) then it's possible that you can realign the thing - again using the front panel controls if it has them. It's hard to describe what to do without seeing the screen and knowing what (if any) menu items are available from the monitors front panel controls...but look for controls that talk about colour alignment or something similar. If the worst comes to the worst and you can't fix it either of those ways - you could reduce the size of the image on the screen (again - assuming you have a monitor menu) so that there isn't any image in the blurry areas. SteveBaker 02:23, 1 May 2007 (UTC)

(Edit conflict) CRT stands for cathode ray tube, so CRT tube is like saying cathode ray tube tube. - AMP'd 02:24, 1 May 2007 (UTC)

Sounds like someone is suffering RAS Syndrome. Vespine 03:33, 1 May 2007 (UTC)

The focus of the CRT is set by (manually) adjusting a fairly high voltage, and it's pretty common for older monitors to drift out of proper adjustment. A qualified person may be able to re-adjust your focus, but please note that it is a high voltage (thousands of volts) so caution is needed!

Also, as SteveBaker said, color CRTs also depend on having three electron beams converge at the same point on the screen; this convergence can drift over the years leading to the red image shifting slightly from the green image which is shifted slightly from the blue image; a casual look might perceive this as an "out of focus" condition as well. Convergence can usually be adjusted (at least a bit) from the monitor's on-screen setup displays.

Atlant 13:18, 1 May 2007 (UTC)

[edit] Non-exploding Sun

When I was at school in the UK we went on a trip to a planetarium. I asked the guy the following question which he was unable to answer, can anyone help?

If the sun is one massive burning ball of gas, why doesn't it explode all in one go rather than burning for millions of years? Thanks, Kirk. —The preceding unsigned comment was added by 91.84.75.27 (talk) 06:31, 1 May 2007 (UTC).

Is the Sun one massive burning ball of gas? A.Z. 06:43, 1 May 2007 (UTC)

No the sun isn't burning in the conventional sense, it is powered by nuclear fusion reactions, which happen in the core where the pressure is high enough. The reason it isn't just blown apart is the massive force of gravity acting on such a big object. Also when it's described as a ball of gas, it means gas in the sense of a state of matter (i.e. not solid or liquid) rather than natural gas or something explosive like that. Stars mainly contain helium (which doesn't burn) and hydrogen, which would burn on earth but requires oxygen, which is not available in space. No doubt better details are in the articles on sun and star.137.138.46.155 07:05, 1 May 2007 (UTC)

(via edit conflict) The tricky word there is "burning" ("gas" isn't entirely correct either, but I'll let it stand for now). Burning implies combustion, which is what happens when you combine (for example) hydrogen gas, oxygen gas, and a little spark to ignite it. What happens on the Sun, on the other hand, is a nuclear fusion reaction where individual protons (aka hydrogen nuclei) combine to form (with a few other processes and particles involved) alpha particles (aka helium nuclei). Now, the reason the sun doesn't explode all in one go is still a rather interesting one, and there are a couple of factors involved: first, nuclear reactions are somewhat haphazard, and require conditions to be "just right" before they'll take place. Thankfully, in the Sun there is so much scope for conditions to be "just right" that it takes place fairly often.

Secondly, the Sun has a lot of fuel, so it has the ability to "burn" for a long time.

Third, the main reason the energy from the nuclear reactions doesn't just cause the whole Sun to explode (aka expand highly rapidly in all directions, ejecting matter and energy at massive rates) is gravity. In a main sequence star like the Sun, the fusion reactions taking place do cause huge outward pressures, that unchecked would cause an explosion (like a supernova), but the force of gravity pulling all the parts of the star in towards its centre counteract those pressures, and things hang in a rather precarious equilibrium. When that equilibrium is disturbed (by a whole lot of factors including the exhaustion/"burning up" of all the hydrogen fuel, several quantum mechanical effects involving neutrinos, and the Pauli exclusion principle, to name a few), the star does "explode", or at least its outermost layers do, in a supernova, which leaves behind a tiny remnant that may be a white dwarf, neutron star, or even a black hole.

(Incidentally, the matter in the Sun isn't really in a gaseous state so much as it is a plasma.)Confusing Manifestation 07:11, 1 May 2007 (UTC)

See Stellar evolution. The sun fuses hydrogen into helium and the rate is determined by the mass of the sun. --Tbeatty 07:12, 1 May 2007 (UTC)

Well, Kirk, I hope you got a gold star for asking a really excellent and insightful question. To complete the picture, the plasma that makes up the Sun behaves like an electrically conducting fluid, so it is affected not just by gravity and pressure, but by a complex interplay of magnetohydrodynamic forces as well. No wonder the planetarium guy couldn't answer your question ! Gandalf61 11:07, 1 May 2007 (UTC)

WOW! I would never have thought that such a seemingly simple question had so much heavy science behind its answer. Now at 34 (a few years after primary school), I finally have an answer. Well done Wikipedia! Thanks everyone and regards from the UK. Kirk

[edit] Formaldehyde

I was reading the article and i found this "Formaldehyde is converted to formic acid in the body, leading to a rise in blood acidity (acidosis), rapid, shallow breathing, blurred vision or complete blindness, hypothermia, and, in the most severe cases, coma or death." I think I understand how everything arises except the hypothermia thing. Can anyone explain how it kicks in place?Bastard Soap 10:52, 1 May 2007 (UTC)

(Off topic story.) Once in chemistry class, we were presented to formaldehyde and our teacher told us "go on, take a breath, it will kill some bacteria for you". Of course, I had to try, so I stuck my nose right to the bottle and inhaled. GAAAAH, how it felt like burning in my throat. Fun thing to do anyway. :-) —Bromskloss 12:52, 1 May 2007 (UTC)

PMID 6955953 looks like a good place to start. I don't have access to the article, was just something I found by keyword search. DMacks 13:19, 1 May 2007 (UTC)

[edit] When did plant roots first evolve?

I tried looking at our article on Root but it doesn't say anything about when and why plant roots first evolved. I would be grateful for any information. Capitalistroadster 11:08, 1 May 2007 (UTC)

in Silurian. You are welcome. Dr_Dima.

Wikipedia is severely lacking in Plant evolution. This major topic should have its own article. Nimur 20:45, 1 May 2007 (UTC)

[edit] Hurricane

What would happen if you exploded a bomb in the eye of the hurricane, or outside it? Would it be possible to stop it with such a device?Bastard Soap 11:13, 1 May 2007 (UTC)

No. Look at Hurricane. The total energy and feeder zone are so huge that it could not be disrupted. As well, our scientific knowledge is not sufficient, we would just as likely do something to strengthen it. --Zeizmic 12:32, 1 May 2007 (UTC)

forgive me for sorta hijacking this question but i think it should also be asked (im courious to know). what about liquid nitrogen?. we know hurrcains are powered by the warmth of the ocean, wouldnt lets say 50 tons of it or more (of course leaving out that cost factor) dropped in the eye walls and eye itself, at least weaken if not disrupt the hurricane? it should cool it down a bit no? User:Maverick423 If It Looks Good Nuke It 15:25, 1 May 2007 (UTC)

Once again the truly incomprehensible scale differences between the lab and the world come into play. A square plate of water one centimeter deep and 67 meters on a side weighs 50 tons. So, even supposing that LN₂ can "dehurricanize" water — that is, cool it enough to make it useless for the hurricane overhead — at a mass ratio of 3000:1 (ridiculous), it takes less than a square 4km on a side to have the top centimeter of water be all that is affected by your cold bomb. A hurricane covers a much bigger square, and the ocean is much deeper. It would cost less to fly the entire population of the affected area somewhere else, with all their personal belongings on additional cargo planes, than to "dilute" a hurricane with such a tactic. --Tardis 15:48, 1 May 2007 (UTC)

wow i dont know why i thought it would work. well lets say it was possable to disrupt a hurricane, what kind of thing would do it? and what kind of energy would be involed in doing this? we said nukes arnt enough (and obvious other reasons too), but what would stop one? only another force of nature? User:Maverick423 If It Looks Good Nuke It 17:02, 1 May 2007 (UTC)

You might be able to shade the hurricane out of existence, say by dusting the air above it to absorb or reflect sunlight. Hurricanes typically lose strength at night, so if you could make a "night" long enough (without at the same time greatly enhancing the local greenhouse effect) you could perhaps starve it over a few days. But the extra heat introduced in the upper atmosphere (or the overall lowered temperature if you reflected the sunlight back into space) might very well cause worse weather somewhere else. The problem is that you're basically fighting energy conservation here: unlike, say, a human, a hurricane doesn't continue to exist because it somehow defends itself from damage or disruption, but rather because it is the natural result of the energies and materials that are present. One might as well attempt to deal with a mudslide by somehow convincing the mud not to go downhill once it is loose and flowing (rather than, say, adding walls, terraces, or vegetation that give it the strength to stay put). --Tardis 17:30, 1 May 2007 (UTC)

Ok, so a hurricane is too huge, but immagine a huge bomb or a small tornado, the answer would still be "highly improbable but we don't know enough to exclude it"?

I doubt it would solve anything. The goal is, as I understand it, to disrupt the spinning so the hurricane stops? It seems more likely that, if you had any effect at all, the thing would just soak up the forces and break up into several subsystems. Imagine two tectonic plates being pushed together, griding along their line of contact. Now imagine imbedding a bomb in the crevice, and blowing it up. The best effect you could have (ignoring the local devestation and the further effects propagated by the system itself; in the case of a storm, fallout from the bomb being carried for miles), would be to crack one of the plates into two smaller plates. It's unlikely, but maybe you'd get lucky. The forces that put the plates there in the first place, and that are pushing them together so hard, are still there and are still going to grind the plates against each other. The result, inevitably, will be earthquakes, but now along multiple fault lines. That's what they mean by it being the result of pre-existing forces. There is a lot of air, and it's the wrong temperature, and it has to go somewhere. It turns out spinning is the best way for it to get where it's going. Therefore it spins, and at best can be made to detour somewhat. Black Carrot 21:16, 1 May 2007 (UTC)

An idea I had for preventing hurricanes is to populate the tropics with floating solar cell rafts, which would collect electricity to sell and thus pay for themselves, and also reflect the light not turned into electricity. If you could have enough of these, they would prevent the water from overheating, which is what causes hurricanes. StuRat 05:03, 2 May 2007 (UTC)

[edit] Building inverters

hi i need ur help in getting results for building my own inverters. its really frustrating going through t6he rigours of finding results for the topic i have just mentioned kindly help me. thanks.

Power inverters (DC to AC)? Logic inverters? Optical inverters?

Atlant 13:22, 1 May 2007 (UTC)

[edit] what is the relationship between hardness and tensile strength of cast iron

Dear sir please give the answer of my question given below:

what is the relationship between hardness and tensile strength of cast iron? —The preceding unsigned comment was added by Pankaj raja (talk • contribs) 12:44, 1 May 2007 (UTC).

We don't do homework, but you might want to study our article on cast iron, paying particular care to the role of carbon and carbides.

Atlant 13:24, 1 May 2007 (UTC)

[edit] Death by Battery

Why do a few people each year die by licking a 9v battery? Is it something in their genes which makes them susceptible to it, or is it just pure chance? If so what is the probability? —The preceding unsigned comment was added by Nebuchandezzar (talk • contribs) 13:41, 1 May 2007 (UTC).

Have you seen a case of this ever happening? Provide a link and someone can then respond better to your question. Seems unlikely. Edison 13:50, 1 May 2007 (UTC)

That sounds like a myth to me. I don't think it's possible to die of 9 V unless you apply it directly to your heart or something. —Bromskloss 14:56, 1 May 2007 (UTC)

Agree, I doubt a DC 9 volt battery could electrocute someone. Maybe the battery casing was broken and chemical poisoning occurred? Nimur 16:18, 1 May 2007 (UTC)

if i recall my electrical trades class correctly, 1.5 volts is enough to stop your heart only if it was directly in contact with it. now i remember making a easy device with my friends that shocked us with 9 volts of electricity when the thing was turned on. it was pretty powerful for 9 volts, however one of my friends took a 120volt shock from a project once and she only made a squeak from it. she started sweating but thats pretty much it. and for me i got shocked with 300 + volts from a experiment with a super weak version of a jacobs ladder. and look at me im still here =)... i think what kills people from voltage was the AMPS if im correct. One Amp can kill a person. im not sure 100% how that amps thing works(didnt pay attention) so someone should be able to clarify it.User:Maverick423 If It Looks Good Nuke It 15:32, 1 May 2007 (UTC)

"Volts gives jolts but current can kill." Okay, the final alliteration is a bit off, but that's how I learned to remember what was what. "A lot of electrical flow" (high current) is what leads to the danger, not "a teeny amount of electricity flowing with great force" (high voltage low current). If I remember correctly, for externally-applied shocks under ideal conditions (minimal skin resistance, etc), lethality can be as low as 30V or so. DMacks 15:39, 1 May 2007 (UTC)

See alsoWilliam Kemmler for an account of the first use of electricity for capital punishment, and [[1]]. Hundreds of electrocutions were carried out smoothly after that one, in which the electrodes may have been incorrectly applied. High voltage AC (over 1000 volts) and several amps were used. Far less current and voltage can be lethal when you are NOT trying to kill someone, but merely come in contact with a frayed electric cord while standing barefoot on a concrete floor. Edison 15:57, 1 May 2007 (UTC)

The amount of current (not voltage) required to stop the human heart is usually cited in the range of a few milliamperes. The amount of potential required to cause that current to flow across the heart varies wildly depending on the circumstances. You can be electrocuted by thousands of volts and be lucky (if you can call it that) enough to have the current find a path that doesn't include your heart. People have survived lightning strikes, which are caused by hundreds of kilovolts of potential, and if you've ever felt a static discharge after shuffling around on the carpet on a dry day, you know what ten to twenty thousand volts can feel like. Alternatively, you could be killed by 120 VAC mains in the right conditions (like standing in the bathtub). Again, it's very dependent on the circumstances. However, 9 V does seem like a stretch. That's a pretty low potential, and even applied directly across the chest I doubt it would cause current flow greater than a few microamperes.

It should be noted, however, that sufficiently high potential can cause large currents, impact ionization, dielectric breakdown and a host of other conditions that may cause severe burns even if you aren't killed. Moral of the story: be careful around high voltages (over a few tens of volts). -- mattb 16:29, 1 May 2007 (UTC)

Jeez why didnt people tell me stuff like this when i was younger? like with the microwave that almost burnt down my home? or before my index finger print was permanitly burnt off from electricity =( well either way hopefully after this we wont hear news of people getting electricuted =) you got to admit though mattb electricity is really really fun to play with (caused some cool explosions and stuff) but defenitly if you take proper safty. Kids dont mess with Electricity! no matter how fun it is....User:Maverick423 If It Looks Good Nuke It 16:43, 1 May 2007 (UTC)

Sure, fun... I remember messing with 1500 F capacitors (not a typo) from a disassembled System/34 when I was a child. In retrospect I'm pretty sure the old man was trying to off me. Well I had better stop this nostalgia moment before it gets on a roll, this is off topic. -- mattb 21:51, 1 May 2007 (UTC)

Whoa! How is it possible to achieve such high capacitances? Are you sure they were that high? Do you have a reference? —Bromskloss 09:55, 2 May 2007 (UTC)

With so many lives at stake, you gotta do some reearch ;-) . If people were dying of 9 volt shocks, there should have been case reports published. Well, I searched PubMed and I've found nothing on fatal 9 volt shock. The lowest voltage for fatal electrocution I found in literature is 46 volts (in Patel & Lo, Stroke (1993), vol. 24 pp. 903-905), five times higher than the voltage in question. So, as Edison and other people have said here already, it seems highly unlikely that electrocution from a 9 volt battery results in several fatalities a year. BTW, look at electric shock article, it gives a pretty good intro to the subject. Cheers, Dr_Dima.

Sticking a battery on your tongue, as a kid at my school once found out, is like to give you an unpleasant shock, a swollen tongue, and the inability to speak properly for a few hours. And a very sheepish expression. Spiral Wave 17:10, 1 May 2007 (UTC)

I've put a 9-volt battery against my tongue many times and never had any sort of aftereffects. As to lethal shocks, I've read (but I can't cite the source, because I don't remember it) that the phase of the heartbeat is an issue. In other words, it's possible that a shock to the heart may be lethal when the same size of shock delivered 1/10 of a second later would be harmless. --Anonymous, May 1, 2007, 22:00 (UTC).

Then if anyone has any ideas, I'm genuinely curious as to what the difference was, because I was witness to this particular event. Perhaps he had a particularly high level of saliva at that moment, that acted as a conductor to get a current flowing? Spiral Wave 17:11, 2 May 2007 (UTC)

snickers* all the good old days when people would fall for anything. anyways assuming you can trick someone into doing this, when they do keep a eye on their tongue, it wiggles and jerks around the whole time the battery is in contact. Wait what am i saying no dont do it to ppl try it on yourself and look in the mirror! shame on you! User:Maverick423 If It Looks Good Nuke It 17:17, 1 May 2007 (UTC)

In reply to the person with the rhyme: Its the volts that jolts, and its the mil(liampere)s that kills. Currents as low as 100mA (maybe even lower) can cause ventricular fibrillation —The preceding unsigned comment was added by 88.111.123.188 (talk) 22:44, 1 May 2007 (UTC).

Implantable cardioverter-defibrillators and Artificial pacemakers that also provide ventricular defribillation are powered by watch batteries. Has a big coil too. So everyone who says current kills, the coil converts current to high voltage to shock the heart. Very little current is required but a large voltage is necessary to make even a lttle current available to the heart V=IR and R is big. --Tbeatty 05:40, 3 May 2007 (UTC)

[edit] color force behavious

I am interested to knoe if the color force exhibits bahavior proportional to 1/r8 (!1 divided by r to the 8 power) and if it does in what range.217.132.19.108 13:45, 1 May 2007 (UTC)

You might read strong interaction, but if I recall, the strengths of the nuclear forces do not have a well-established, well-agreed-upon direct radial dependence. I believe there are many other factors at play in the situation. Nimur 16:20, 1 May 2007 (UTC)

In fact the colour force gets stronger with distance, which is why you never get isolated colour charges.137.138.46.155 11:39, 2 May 2007 (UTC)

I realized that the color force has dependencies that are reversed to the distance. However, I believe that there must be some dependency that reduces with distance and involves r to the power of eight. Does anyone know of a research that investigates this part of the color force?217.132.81.98 12:14, 3 May 2007 (UTC)

[edit] Curvature of the neck (cervical spine)

Somehow I ended up going to a chiropractor for an assessment and he took a bunch of xrays. (don't ask) ^{or do if you like}
He came back and showed me the xrays and on my neck he showed how I had no curviture in my neck at all! And I could see it on the xrays myself! He said my neck had 0° curviture and that a normal neck (showing me another xray) had about 18° curviture. He's warned me of some negative effects of this and says he can treat me and give my neck some curviture in about 3-6 months, and I don't know if I can trust him (he is a chiropractor after all, and not a "Conventional" doctor).

Seen as you can't give medical advice my questions are...

What is considered a "normal" curviture in the spine, particularly the neck (cervical spine)? and/or
Specifically what kind of doctor would be good to evaluate this?

Thanks so much for any help! —The preceding unsigned comment was added by 138.130.23.133 (talk) 15:01, 1 May 2007 (UTC).

Don't know, but the quackwatch has a good dedication to being anti-chiropractor. Why don't you see a general practitioner about it? Couldn't he or she do it, or, if not, refer you to somebody afterwards. [Mac Δαvιs] ❖ 16:41, 1 May 2007 (UTC)

Maybe this is an obvious question, but doesn't the curvature of the cervical spine vary depending on how you bend your neck ? That is, couldn't the chiropractor have intentionally put you in a straight position for the X-ray and then concocted this BS story to drain your bank account ? Also, X-rays carry some (fairly low) risk of causing cancer, so I would only get them from a real doctor when medically necessary. StuRat 04:55, 2 May 2007 (UTC)

This little google search is useful, to some extent. It seems likely that if you have a sore neck, getting the curvature of your neck sorted might be useful, but there is some question as to whether it needs sorting if you don't have any pain. However, of course, seeing a GP and explaining exactly what symptoms you have, and exactly what the chiropractor told you, is what you should really, really do. Chiropractors vary, from those who just use the useful, proven bits that work to solve appropriate problems (see this forum, for instance), to those who believe germs are a symptom, not a cause, of disease. Getting an orthodox view from a 'real' doctor would be a very good idea. Skittle 13:41, 2 May 2007 (UTC)

[edit] Determining the critical angle of the substance glycerol/glycerine (I think it's the same thing)

We did an experiment in class to find out what the critical angle of glycerol is. Some of my mates say it's 42,57°, but I figured it to be 132,57°. The two numbers differ by 90°, so I dunno if I just made a common error when I took the info.

Anyways, glycerol (glycerine) has a refractive index of 1,4729.

We had a beam of light reflect at 90° from a border between air and glycerol.

Can anyone please help me with this experiment? I really need to know this answer.

I tried using snell's law, n1sinθ1 = n2sinθ2, but when I substitute the information into the formula, 1sin42,57° = (1,4729)sin90°, it just doesn't make any sense. Maybe I did something wrong? Please please take some time to help me with this. Maybe you have an example in your physics text book, or you did this experiment yourself before? Any information will help.

Thanks in advance :D

► Adriaan90 ( Talk ♥ Contribs ) ♪♫ 16:36, 1 May 2007 (UTC)

I'm afraid you've got it wrong. Look carefully at the drawing in Snell's law, and you will easily spot your mistake. Good luck, Dr_Dima.

So, basically, there's not much to it? ► Adriaan90 ( Talk ♥ Contribs ) ♪♫ 17:49, 1 May 2007 (UTC)

What do you mean by "not much to it"? You've got a problem to solve. Here on Wiki we do not solve homework problems, we help you to solve them yourself; that is how you learn. I'll give you a hint, though. What are subscripts "1" and "2" there for in the Snell's law? They denote, respectively, the first medium and the second medium through which the light goes. Which is the first one and which is the second one in your case? What is the refractive index of the first one and of the second one? At what angle to the normal the light is going in the first one and in the second one? Be careful writing these things down, and you'll spot the mistake you made when using Snell's law. Oh, and after you find the mistake, you may also take another look at the drawing and think why the angle cannot be anything like 132°. Good luck. Dr_Dima

Ok... sorry and thanks, lol. I've spotted my problem. I substituted the values of the different refractive indices as well as the different angles into the wrong parts of the equation, because I assumed the light beam was traveling from air to a surface with glycerol, which is false. The beam is traveling from glycerol to a surface with air, which makes n₁ = 1,4729 and Θ₁ would be the critical angle (42,57°). n₂ = 1 (because it's the refractive index of air at normal temperature etc., rounded) and Θ₂ obviously is 90°, because we are using the critical angle, thing, so we don't even need to measure it. Lol. Anyways, so it happens that (1,4729)sin42,57° = sin90°, which is 1 = 1, and there we know that all the information are correct. Thanks for all your help ; ) ► Adriaan90 ( Talk ♥ Contribs ) ♪♫ 21:46, 1 May 2007 (UTC)

You are welcome. Best regards, Dr_Dima.

[edit] Calcium in a bone

How muh Calcium is there in an average 1cm^2 section of bone? Yes, I know it varies between differnt bones and different parts of bone. It probably varies between people too. I just want a rough idea, but not too inaccurate. So..? —The preceding unsigned comment was added by 172.203.7.239 (talk) 19:42, 1 May 2007 (UTC).

Hi, in the future, could you please label your titles more concise, "science" doesn't explain anything at all about your question and pretty much makes it so anyone only using the watch list ignores you. Thanks! --KittenMya 20:04, 1 May 2007 (UTC)

I didn't see the answers in our bone density or osteoporosis articles, so will take a wild guess, instead. Since bones are hollow, containing marrow and such, I would guess they are maybe 10% calcium. So, then you would have 0.1 cm² calcium per cm² of bone. Bird bones, though, are considerably less dense (to keep the weight down), so would likely have less calcium. Perhaps elephant bones would need more calcium to support their weight. StuRat 04:49, 2 May 2007 (UTC)

Good grief. I thought this was the science reference desk, not the wild guess reference desk.

Gray's Anatomy, 1958 edition, says that "the bone 'salts' constitute the mineral constituents and confer on the bone its hardness and density. The most important constituents of bone 'salts' are calcium, magnesium, phosphate, carbonate, chloride, fluoride and citrate. The mineral substances of bone may be obtained by calcination, which destroys the organic matter. The bone retains its original form but is white and brittle, has lost about 1/3 of its original weight and crumbles under the slightest force." So in other words, in the solid matter of a bone, about 2/3 is mineral components and calcium is listed first among these. This would make sense if the calcium is something like 1/8 to 1/3 of the total bone mass, say.

I also note that Encarta's online article "Bone (anatomy)" says that the bones make up 14% of the weight of the human body, and Wikipedia's article Abundance of the chemical elements says that 1.5% of the human body is calcium. It would therefore seem that bones are about 1.5%/14% = 11% calcium. However, I'm dubious about these numbers. First, I found the same table of elemental abundance on another web page but identified as referring to the composition of the human body without the water, which obviously makes a big difference. Second, they could be defining "bone" differently, e.g. one counting only the hard stuff (as Gray's Anatomy evidently was) and the other including the marrow. And finally, none of these sources gave a range of values, but obviously people will vary.

Both of these calculations only with towards a value for the fraction of bone that is calcium, not the quantity of calcium per unit volume of bone as asked for (well, actually the original poster quoted an area unit, but I assume volume was intended). Unfortunately I did not find anything that stated the density of bone. In any case StuRat's point about hollow spaces in bones is relevant here: it's going to make a big difference whether you're talking about bone (the hard substance) or bones (including everything) or specific bones or what.

--Anon, May 2, 2007, 07:08 (UTC).

bone density is around 850

1cm^3 of bone is 1ml, which is therefore just under 1g :) If bone is slightly more than 10% calcium, that sugests there is about 100mg of calcium in 1cm^3 of bone, about the same as there is in 100ml of milk :) But my opinion probably doesn't count around here now, so can someone else work out where (and if) I have gone wrong :( HS7 17:04, 2 May 2007 (UTC)

[edit] What Is the Greenish Layer of Some Hard Boiled Eggs

With hard boiled eggs, the yolk has a thin greenish layer where it is in contact with the white, while the inside of the yolk is yellowish as expected. The eggs are fresh. The cooking time is about 15 minutes. What is it that gives this green-like color?--JLdesAlpins 20:27, 1 May 2007 (UTC)

Iron and sulfur. --LarryMac 20:31, 1 May 2007 (UTC)

Thanks LarryMac. I will suggest that the section "Problems when cooking eggs" be moved in Hard_boiled_egg.--JLdesAlpins 20:36, 1 May 2007 (UTC)

15 minutes for boiled eggs? Wow, you are overcooking them to death! --24.249.108.133 04:18, 2 May 2007 (UTC)

Ya! Can't deny that now.--JLdesAlpins 16:35, 3 May 2007 (UTC)

[edit] Using magnetism to recover coins and jewelry

I have been using a heavy lift magnet in a local lake and in a canal to recover fishing rigs and various metal things like bikes from the waters. I realize magnets only work on ferrous metals but wonder if there is a way to induce some magnetism into more valuable objects like coins or jewelry. Is there an electrical magnet or device that generates enough of a magnetic field that it would attract nickel, gold etc. Thanks —The preceding unsigned comment was added by 137.246.193.233 (talk) 20:40, 1 May 2007 (UTC).

Nickel should not be a problem because it is ferromagnetic. You might want to see that article, which has a list of ferromagnetic materials. Nimur 20:58, 1 May 2007 (UTC)

Hence the obvious solution, move the lake to Canada, where almost all coins are either nickel or steel! --Anonymous and very silly, May 1, 2007, 22:07 (UTC).

Yes of course! You can use lc ac (alternating current) to induce currents in the non ferromagnetic object and ~~attract~~ agitate it.

Sorry, eddy currents repel rather than arract non-ferromagetic conductors, see Magnetic levitation#High-frequency oscillating electromagnetic fields. --mglg_(talk) 23:31, 1 May 2007 (UTC)

the repelling force might be enough to stir the mud around the object, and so make its location noticeable.Polypipe Wrangler 23:35, 1 May 2007 (UTC)

A metal detector uses alterneting currents to detect non ferrous metals. You could use one in a lake to find your coins, although you would have to use another means to separate them from the mud.GB 00:30, 2 May 2007 (UTC)

Whilst lakes and canals attract bikes, shopping carts, bedsteads and bodies, I doubt they will ever be fruitful in terms of jewelry and coins. You'd be far better off employing a metal detector in parks and on beaches.--Shantavira 06:52, 2 May 2007 (UTC)

[edit] molarity question. help!

i have a 250 mL beaker, but I do not know how many mols of 4.00 M solution I should use to make a .500 M solution. Any suggestions? Thanks! —The preceding unsigned comment was added by 76.188.176.32 (talk) 20:47, 1 May 2007 (UTC).

What is the molecule/compound you're trying to solutinate? --KittenMya 20:56, 1 May 2007 (UTC)

NaOH Does this help??

Hi, I believe the formula for this is grams of NaOH = (solution required, ie .500) * (molecule weight, ie 40) * (amount to produce, ie 250ml) / 1000, though aplogies if I misread your question, I'm tired. --KittenMya 21:19, 1 May 2007 (UTC)

I don't understand how that all cancels out, and from where did the 1000 come?

The identity of the solute is irrelevant here. Do you really want to know "mols" of the 4.00 M solution, or maybe a volume (for example "mL") instead? Think about what molarity means, and what units are represented by "M". DMacks 21:26, 1 May 2007 (UTC)

Yes! I want to know the mL.

I have thought that perhaps I can find the mols of .50M solution by taking .50=mols/.250L which gives me mols=.125 mols NaOH But, I don't know where to go from there, and I don't even know if that is right.

Maybe I should use that mol number to do 4.00 M=.125mols/unknown L.... to find the mL? Any comments help.

Good! You found you need 0.125 mol to disolve in the 250 mL; that's equivalent to (the same ratio as) 0.5 mol dissolved in 1000 mL (= 1 L), and "mol per L" is the definition of the "M" unit of molarity. So now you're on the right track again: you need to figure out how much volume contains that 0.125 mol if it is a 4 M solution.

You can often check to make sure your math is at least "reasonable" if you look at the units you are using. Math with unit symbols is the same as numerical math: in your first thought, you divided a number of mol by a number of L, which gives an answer that has units of "mol divided by L", which is the fraction "mol/L". DMacks 21:44, 1 May 2007 (UTC)

Well, I understand what you're saying. But, if .5mol/1L= .5M .... then is the problem set up as .125mol/X=4.00M? The answer just doesnt seem to make sense.

Its such a small answer in liters, that the number seems completely wrong when put into decimals, doesnt it?

rolls eyes* OK, guys. Forget about moles. A concentration of 4 needs to be diluted to a concentration of 0.5. 4/0.5=8 therefore, you need to dilute your 4M stuff 8-fold. For example, take 10ml of your 4M solution and add 70mL of water. Et voila, 0.5M solution. If you need 250mL, divide 250mL by 8 = 31.25mL. So add 31.25mL of your 4M solution to 31.25x7=218.75mL of water. In summary, 31.25mL 4M solution + 218.75mL water = 250mL 0.5M solution. Aaadddaaammm 00:38, 2 May 2007 (UTC)

Actually solutions can contract and expand under certain circumstances. Instead of using a specific amount of water, use enough water to fill the 250 ml beaker to the right line (after putting in 31.25ml of the solution to dilute). That gives the best result (beakers are most accurate at their full volume) —The preceding unsigned comment was added by MacGyverMagic (talk • contribs) 12:23, 2 May 2007 (UTC).

I have to completely disagree with you here. Sure, when you mix two different liquids, they can not quite add up. Eg 50ml water + 50mL ethanol = 95ml or so. But here we're mixing two different aqueous fluid - 50ml + 50ml WILL = 100mL. As to using the measuring marks on the side of a beaker, you have to be kidding me! These are not very accurate at all. You'd be much better measuring each aliquot in a measuring cylinder or pipette. Alternatively, a 250mL volumetric flask would be another good option if you add 31.25mL of 4M stuff then top up to the measurement line with the water. Aaadddaaammm 09:54, 3 May 2007 (UTC)

[edit] Eyebrow

What are the muscles that raise the eyebrow? My anatomy textbook doesn't really cover it. As far as I can tell, the muscle resposible for raising both eyebrows at once all along the forehead is the frontal belly of the occipitofrontalis. I can't seem to find the one that raises just one eyebrow way off to the side, though. Any suggestions? Black Carrot 21:23, 1 May 2007 (UTC)

I think the answer may be Occipitofrontalis muscle like you think. Look at facial muscles for the choice of muslces on the face, but there are no others in the area. In order to move just part of the eyebrow, only part of the muscle contracts. Different nerve fibres go to different parts of the muscle giving a finer control. GB 01:39, 2 May 2007 (UTC)

Why do eyebrows even exist? I mean is there an evolutionary advantage linked to them?Bastard Soap 18:59, 2 May 2007 (UTC)

Well, one obvious advantage is that they help keep sweat from dripping into your eyes while you're trying to outrun a predator. Don't know if that's anything like real reason, though. --Anon, May 2, 2007, 22:52 (UTC).

[edit] Dropstones and metals. Or just rubbish.

http://en.wikipedia.org/wiki/Dropstone

Above is a piece about dropstones which are interesting anomalies.

But what will happen millenia hence with the metals (ships and such) we have dropped on the ocean floor. Or metallic rubbish like stainless steel injection needles in our land fills.

Will they be absorbed and become little gaps in the rock or be preserved in the sedimenta.

Does steel under pressure degrade rust or defom ?

Sensible question. What will happen to our non organic rubbish millennia hence.

Thanks

Paul

81.86.166.234Paul.Mckenna at mac .com81.86.166.234 21:59, 1 May 2007 (UTC)

I presume a mechanism akin to fossilisation. As these metals corrode (and presumably the corrosion products get washed away) there is a race between that effect and the effects of sedimentation covering them up and shutting out the water and oxygen to preserve them. Where rates of sedimentation are high, and if the resulting rock is relatively impervious to water - then you'd end up with a kind of fossil of the metal chunk - if not then nothing. It's hard to say - but it almost certainly depends a lot on the rate of corrosion versus the rate of rock formation above them. SteveBaker 22:35, 1 May 2007 (UTC)

If the metal is buried where there is no oxygen, say along with much organic matter, it may stay unmodified for millions of years, but more normally the metal will react with oxygen, carbon dioxide, silica, or suphur and form more natural minerals that the artificial metal. You can expect metals such as gold or platinum to be dug up and recylcled! Land fills are likely to erode away in the distant future and so the metal content will be spread in to sediments elsewhere, but on the ocean floor may stay where they fall. GB 01:33, 2 May 2007 (UTC)

[edit] Nuclear hurricane

a question above about hurricanes got me thinking... what if a couple of nukes were dropped or detonated on a hurricane. the awnsers above stated that the hurricane wouldnt be dissapate, so there for would that mean that instead of having just a regular old hurricane comming our way, it would be a hurricane with nuclear fallout bearing down on us? and if thats the case wouldnt this be used as another weapon of mass destruction? and *of course jokeing* would the rain glow as it falls to the ground? User:Maverick423 If It Looks Good Nuke It 22:27, 1 May 2007 (UTC)

Yes, it would spread radiation all over the place, and probably into the jet stream. Titoxd^{(?!? - cool stuff)} 22:29, 1 May 2007 (UTC)

The rain wouldn't glow. It would probably be black, like the rain over Hiroshima was. As a WMD it would be less effective and less controllable than just dropping the bomb on the designated target. --24.147.86.187 23:05, 1 May 2007 (UTC)

ouch sounds like a bad day then. but as a WMD most hurricanes move to the US, a terroist can detonate a nuke long before and we might not be able to find out about it till its too late. but then again who would risk killing them selvs when the jetstream takes the fallout to them =) User:Maverick423 If It Looks Good Nuke It 13:15, 2 May 2007 (UTC)

It's also improper to assume that the hurricane itself becomes radioactive. Rather, the debris from the bomb (and there's not much, since it's an aerial detonation over ocean; you're not making dirt into radioactive dust) spreads into the hurricane, gets caught in raindrops, and falls (thus the black rain at Hiroshima). Most of the radioactive material, therefore, hits the ocean under the detonation. You can't nuke a hurricane a week before it reaches shore and expect it to be a legitimate (nuclear) threat. It'd be a panic threat, sure, but it would likewise (likely) be less effective than just using a nuke in the usual fashion. — Lomn 15:15, 2 May 2007 (UTC)

[edit] Temperature of the sun

Does the sun get hotter year after year like other stars? If so, what is the effect on earth? —The preceding unsigned comment was added by 74.244.99.200 (talk) 22:52, 1 May 2007 (UTC).

Overall, in a multimillion year time span, the sun will be getting cooler. See red giant and white dwarf. However, in a reasonable time span of thousands or hundreds of years, it is variable and I am not sure a trend is known. If the trend is known to follow solar insolation (which is only found due to correlations with sunspots and the earth's orbit. Here's a graph of the theoretical solar insolation, on the top line in the graph[2]. [Mac Δαvιs] ❖ 02:09, 2 May 2007 (UTC)

If you mean "like other stars" as a main sequence-type change (see the Hertzsprung-Russell diagram), then yes, the Sun does get hotter. It's not really a year on year type of change though; it's measured over thousands and millions of years. Stellar evolution is the article you want. It will continue to steadily get hotter until it becomes a red giant.

As for its effects, it means the habitable zone around the Sun moves outwards. This is an imaginary ring around a star where a planet would be at the right temperature for liquid water. The Earth is 'lucky' in that we're always in the Sun's habitable zone - when the Sun formed we started just beyond the middle of it, and by the end of the Sun's lifetime we'll be just near the inner edge, because the ring gradually moves outwards as a star heats up; but we'll never lie outside it (at least before it all turns a bit nasty and red giant-ish). So in the far future the Earth will get considerably warmer, though not uninhabitable. It's not an effect you'll notice over a century or two though (though there may be other types of cycle that affect things on those scales - you should probably check Solar variation if that's the type of change that interests you. Global warming arguments and so on, in there). Spiral Wave 02:05, 2 May 2007 (UTC)

I stated that the sun would gradually cool and enlarge into a red giant, while you said it would heat. I thought that the star would expand enough that the increase in heat is overplayed, and overall the temperature would grow lower, while the amount of heat would grow higher. [Mac Δαvιs] ❖ 02:15, 2 May 2007 (UTC)

Well, perhaps once it starts getting closer to being a red giant, in a couple of billion years time. But in the current epoch I would have assumed the increase in temperature outweighed the difference - I thought it was still in the heating phase David Ruben pointed out below (albeit not as fast now). I'm quite prepared to be wrong though, and I take your point that eventually, as it grows the effective temperature will drop, well before it becomes a red giant. Nonetheless, I'm quite certain that the habitable zone moves outwards for the bulk of its lifespan (a process that isn't finished yet) and that would imply that the temperature at any given distance is increasing, which is still relevant to the second part of the question. So as David said below, it gets cooler, but we get hotter. Spiral Wave 03:10, 2 May 2007 (UTC)

It's misleading to say that a star cools when it becomes a red giant, as I understand it. The surface cools, but that's only because it's moved out so far. Inside the star is hotter than before, which is why it's giving off more heat than before. --Anon, May 2, 2007, 07:18 (UTC).

That's why I said the effective temperature. Thank you for making it clear though, I'm really not doing a very good job of this. Spiral Wave 09:18, 2 May 2007 (UTC)

The sun goes through various Solar variation cycles (e.g. solar cycle of sunspots). Over the longer term it is thought to have heated up by 40% since it reached the main sequence 4.6 billion years ago (see Star#Main sequence). Finally it will cool as it approaches the end and enlarges to form a Red giant. Whilst its surface temperature will then be lower, here on earth its reducing proximity will cause the earth to evaporate off before it is engulfed. David Ruben ^Talk 02:20, 2 May 2007 (UTC)

The sun has many cycles. I believe there is a cycle that correlates well to earths ice ages and the sun is currently warming. There are shorter and longer cycles in addition to the main sequence cycle. --Tbeatty 06:07, 2 May 2007 (UTC)

[edit] Lightbulbs

Why are lightbulbs measured in watts and not ohms? If I change the number of volts, does the number of watts not change for a lightbulb regardless of its designated number of watts? J Are you green? 23:18, 1 May 2007 (UTC)

Well, they are specified both in wattage and voltage - so you can figure out the resistance - but remember this is an AC powered device - and it's resistance varies with temperature - it's not as simple as you think! Since (as you say) you can calculate any one of watts/ohms/volts if you know the other two, they could have specified any two of those numbers. My guess as to why they did it is because people care about how much current they are consuming - not about some more abstract thing like resistance. The other problem (I suppose) would be that if you rated bulbs in ohms, lower numbers would be for brighter bulbs - which might be confusing. The whole rating system is a mess anyway - we don't really care what wattage or resistance the bulb imposes - what we mostly care about is how much light it produces. In that regard, a 40 Watt incandescent bulb produces much less light than a compact florescent lamp that consumed 40 Watts. SteveBaker 23:27, 1 May 2007 (UTC)

Yes, it would make a whole lot more sense to measure light, but for watts/ohms/volts, the lightbulb itself is the source of resistance. That is, if I take a 40 W bulb and turn it on with a 1 V power source, then increase the power to 2 V, won't the bulb become an 80 W bulb since the bulb's resistance is constant. If I understand this correctly, the number of watts has nothing to do with the bulb - only the resistance. As for your other point about lower numbers and brighter bulbs, why not measure in Ω^-1? I suppose none of this has a real application, but I am just curious to know. J Are you green? 23:38, 1 May 2007 (UTC)

A 1 V light globe is quite unusual - particularly one that consumes 40W. However if you increased the voltage to 2V and the resistance remained the same, the current would double, and the power consumed would quadriple, so it would burn 160W. Don't expect any light globe would work at double its rated voltage however. The filament would overheat and melt. GB 00:35, 2 May 2007 (UTC)

Oops. I meant in in theory, not as a real example, though. J Are you green? 00:43, 2 May 2007 (UTC)

Nobody seems to have mentioned the fact that the bulbs you put into your light fixture are expected to be operated at a fairly constant mains voltage, so the wattage rating does make a little sense. -- mattb 00:42, 2 May 2007 (UTC)

I realise that, but the wattage is independent of the lightbulb, isn't it? So why measure the bulb in something that it itself does not control? J Are you green? 00:45, 2 May 2007 (UTC)

What's the difference? People don't have a better idea of what a lumen is as opposed to 40 W. -- mattb 00:48, 2 May 2007 (UTC)

Well, say I take a bulb of 1 W at 1 V. If I then reduce the voltage to, say, .5 V, then the power likewise decreases. The watts never had anything to do with the actual lightbulb, only the bulb's resistance. Also, I really don't see how lumens tie in to this. J Are you green? 00:59, 2 May 2007 (UTC)

Well, the filament's resistance is a result of physical parameters like material composition, dimensions, temperature, and some quantum effects... It has plenty to do with the bulb itself. I'm not sure what your question is at this point. -- mattb 01:22, 2 May 2007 (UTC)

Yes, but it has equally plenty to do with the power source. J Are you green? 01:39, 2 May 2007 (UTC)

Getting back to the original question, changing the voltage will change the watts consumed for a globe, however the rated power in watts should apply if the rated voltage is used. GB 01:28, 2 May 2007 (UTC)

I cannot see why a manufacturer would stamp "80 W" on a bulb if its watts depends on the power source. That is the original question. J Are you green? 01:39, 2 May 2007 (UTC)

Yes, the bulb has a fixed resistance (more or less), but the resistance is not the only important attribute of the bulb. The bulb is designed to operate at a particular power. a one-ohm bulb designes to operate a 3V ( a flashlight bulb) is very different from a one-ohm bulb designed to operate at 120V. (desk lamp bulb). put 3V across the big buld, get no light. put 120V across the flashlight bulb, get lots of light -- for about one millisecond. The Wattage is a measure of the designed power output the bulb can sustain. -70.177.166.200 02:12, 2 May 2007 (UTC)

So, you are basically saying that the number of watts on a bulb is not an actual attribute of the bulb, but rather the power at which the bulb was designed to operate. So, the number of watts is not a necessarily constant but rather a recommendation given the bulb's resistance and its intended voltage. I see... J Are you green? 03:28, 2 May 2007 (UTC)

Correct. If you operate the bulb at a lower wattage, the filament temperature will be too low to emit white light. The light will be redish and you get less lumens per watt. If you operate the bulb at a higher wattage, the filament will be hotter, the ligh will be bluer, and the filament will burn out faster.-Arch dude 05:49, 2 May 2007 (UTC)

In any case the resistance of a light bulb is not constant either -- not even close. Someone mentioned above that resistance depends on temperature. Let me go into that some more. I just took a couple of light bulbs rated for 120 V. One is a 150 W bulb so you would expect its resistance to be 120×120/150 = 96 ohms; the other is a 60 W build so you would expect 240 ohms. I put a multimeter to them at room temperature and they were 6.3 and 18.5 ohms respectively. (And I checked the multimeter against some known resistances too; it was right.) Which means the 150 W bulb when first switched on draws more current, all by itself, than a 15 A circuit will take. But in a small fraction of a second, before the breaker can trip, its resistance rises to 96 ohms. If you operated it 9/10 of the voltage, 108 V instead of 120 V, then you might expect it to pass 9/10 as much current and so consume 150×9/10×9/10 = 121.5 W; but actually the resistance would be less than 96 ohms and it might consume say 130 W or 140 W. (But as noted above, it would burn cooler and thus less efficiently.)

In short, quoting the resistance would really be no more practical than quoting the wattage is.

--Anonymous, May 2, 2007, 07:55 (UTC).

Interresting... that satisfied pretty much anything left for me to doubt about the purpose of a watt rating on a lightbulb. Thanks! J Are you green? 21:24, 2 May 2007 (UTC)

Marking the lamps with the wattage is a convenience, given that, within a single geographical region, we all operate the lamps on pretty-much the same voltage. The scale of the number also works out conveniently (so we can speak of 5 watt and 150 watt lamps and not 40 mA and 1.25 amp lamps). We could instead have marked them in light output, but then you'd have no clue whatsoever how many lamps can be connected to a single electric branch circuit before the fuse/circuit breaker would blow.

Atlant 13:41, 2 May 2007 (UTC)

Incandescent light bulbs are best understood in terms of energy balance: the energy drawn by a bulb must be equal to the total cooling experienced by the filament (as it throws off radiation). Resistance in most materials (including filaments) increases with temperature, as Anon observed; moreover, radiative output increases dramatically with temperature. As such (pretending that the bulb has a single temperature and resistance), as temperature increases power input $V^2\over R$ goes down and power output

A εσ T 4

goes up. There will therefore be some temperature at which they balance, and that's the operating temperature of the bulb (which determines its color, etc.). If you reduce the voltage, you will (for any resistance) reduce the power, and so that temperature will be lower; if the temperature is lower the power output must decrease. This makes sense; "pushing" a mostly-inert object (like the filament) less hard should produce less result. (I make this point because Anon suggested that the power might go up; it won't.)

Interpolating to respond to this point alone, I only said that lowering the voltage will not reduce the power as much as you would expect if the resistance was constant; I did not mean to suggest that it might increase it. --Anon, May 3, 04:46 (UTC).

As for the original question, there is no single number that describes the bulb alone that would be useful in this context, precisely because of the dependence on the power source that the OP cited. So we mark bulbs with a practical number that is correct in normal use: it says how much heat the bulb produces (since all light it puts out indoors will eventually become heat) and how much it costs to operate it, as well as (through personal experience) giving us a sense of how much light to expect. If I may append my own question here, someone please look at color temperature and tungsten; obviously bulbs must operate below 3700K, but they seem significantly "whiter" than the corresponding point on the color plots; "white heat" is typically associated with temperatures of at least 5000K. Is it just a physiologic effect that such bulbs appear white, or is there some physical reason for the effect? --Tardis 15:55, 2 May 2007 (UTC)

Having experimented with coming in from outside to an enclosed room lit only by an incandescent bulb, and with moving about a house lit with a combination of energy saving bulbs and incandescent bulbs, I can say that incandescent bulbs are very yellow. Your eyes (or brain) adjust, but they really are quite yellow. Skittle 21:05, 2 May 2007 (UTC)

Yes. If you look at photographs taken by sunlight and by ordinary incandescent light bulbs, the color difference is quite obvious. The brain adjusts. --Anonymous, May 2, 2007, 22:56 (UTC).

Strangely enough, I experimented for that, too. I used a color control card, so I actually have quantative measurements. Here's an example of the color cyan as a percentage of C/M/Y in sunlight and incandescent lightings:

Sunlight:70.3704/29.6296/0

Incandescent:58.0420/12.5874/29.3706

For incandescent lighting, cyan was nearly 30% yellow! J Are you green? 01:24, 3 May 2007 (UTC)