Wikipedia:Reference desk/Archives/Science/2016 November 20

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November 20

Does the vas deferens contain stem cells?

Does the vas deferens contain stem cells?

Also, for the record, my question here is geared towards the human vas deferens. Futurist110 (talk) 01:10, 20 November 2016 (UTC)

I think not, at least not in any significant number. But human vas deferens fibroblasts can be cultured, and those fibroblasts can be used to generate induced pluripotent stem cells. [1] - Nunh-huh 01:17, 20 November 2016 (UTC)

OK. Futurist110 (talk) 05:14, 22 November 2016 (UTC)

Artillery question

Would an artillery shell which is filled mostly with high explosive but also contains buckshot (or ball bearings) to enhance the fragmentation effect still be considered a HE shell, or would it be classified as a shrapnel shell? Or would it be considered a hybrid between these types? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 05:47, 20 November 2016 (UTC)

I can't find any evidence of such a shell existing, at least as a standardized piece of equipment. Since the name would be arbitrary to begin with, there's no answer to give unless an example can be found. Someguy1221 (talk) 06:25, 20 November 2016 (UTC)

During the Israeli-Lebanon war of 2006 (or 2007, I forget), the Lebanese used rockets with HE/buckshot warheads similar to what I described here -- I wonder how come nobody mentions this? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 06:37, 20 November 2016 (UTC)

Lebanese army equipment was all manufactured in the US, France and Russia, none of which (as far as I can figure) make any rockets or artillery shells like the one you describe. If the Lebanese used one, I would thus assume it's not a standardized piece of ammunition, which may be the reason for the lack of information. Someguy1221 (talk) 06:48, 20 November 2016 (UTC)

I'm assuming you're aware of the Beehive anti-personnel round? Not exactly what you're asking, as it seems it doesn't actually have an HE charge, but perhaps interesting nonetheless. Fgf10 (talk) 16:35, 20 November 2016 (UTC)

Well, the beehive round is more like the "normal" shrapnel round in that it relies on the shell's velocity to scatter the flechettes -- I was asking about a round which uses (mainly) the explosive force of the filler to achieve this. 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 07:29, 21 November 2016 (UTC)

Some information at Shrapnel shell#Modern era, but it seems that most modern HE shells depend on the fragmentation of the external body of the shell to throw out damaging pieces of metal. The original shrapnel shells, not much used after World War I, had a small high explosive "bursting charge" to scatter the solid shot inside, which were generally a bit larger than a normal ball bearing and much larger than buckshot. Alansplodge (talk) 22:41, 20 November 2016 (UTC)

Yes, I know this -- what I'm asking about is a hybrid of the two, in which most of the wounding effects come from the ball bearings (rather than pieces of the external body, although they also contribute) as in a shrapnel shell, but the force which propels these comes mainly from the explosive charge as in a HE shell. (I'm sure the Lebanese used these during the 2006 war with Israel, I saw the reports on both Fox and CNN -- I wonder why there's no info about it?) 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 07:29, 21 November 2016 (UTC)

So you're saying that there are in fact artillery shells more-or-less like I described, and that these are called "all-round shrapnel shells" -- is that correct? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 23:31, 21 November 2016 (UTC)

Note that terrorists, by definition, are NOT civilians but are classified as illegal combatants -- but other than that, this is useful info! 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 01:26, 22 November 2016 (UTC)

In the specific 2006 conflict to which you refer, the combatant forces did not principally include the Lebanese Army, although a state of war existed and the national army did see some combat action. Review the article on the 2006 Lebanon War, and the South Lebanon conflict (1985–2000), for some historical information on this complex region and the various participants in its conflict.

Perhaps you are asking about improvised explosive devices - there are a near-infinite variety of such devices, which take nearly any form that can cause any manner of destruction that the creator can conceive.

Here's a great book that I keep in my library: The Flipside of COIN (a survey of counter-insurgency tactics in Lebanon and their ultimate failure between 1978 and 2000). That book gives you some fantastic insight into the versatile opponent(s) and their diverse tactics. If you specifically are looking for a book on the 2006 conflict: We Were Caught Unprepared, another research paper on the Israeli military's more recent misadventure, published in the same US Army Combat Research Institute monograph series.

I would point out that the resistance forces in Lebanon were not notorious for antipersonnel or shrapnel explosive mines used against infantry. Rather, their trademark was to use comically large antitank mines, tactically hidden covertly, to blow holes the size of city blocks in specific high-value targets like enemy area-commanders. Quoting, id:

"As the three-vehicle convoy made its way back down the treacherous mountain road to IDF headquarters in Marjayoun, (Brigadier General Erez Gerstein)'s Mercedes rounded a jagged curve. At precisely the same moment, a massive improvised explosive device (IED) detonated next to the car. The explosion ripped through the Mercedes, engulfing the automobile in flames. Abu- Rish, El-Kabetz, and Roeh were blown out of the vehicle and mortally wounded as the Mercedes tumbled over a cliff with Gerstein still inside."

In other words, the standard signature tactic wasn't a shrapnel charge, improvised or otherwise - the signature tactic was to somehow acquire and use comically large quantities of high explosive - the sort of detonation charge that could flip a seventy ton Merkava tank upside-down - and to somehow get those charges buried underneath highly-protected, high-value enemy targets.

The other element you referred to - the rockets - probably used standard-issue fragmentation charges delivered by a variety of standard- and custom-made Eastern-bloc (and other, clandestinely-acquired) rockets of unknown origin. It is a sad and scary truth that there exist many factories in our world who still build such devices. The OP's statement - "nobody mentions this" - because you won't commonly find people talking about such unfortunate topics loudly and in public. A great resource for the interested researcher is the Combined Arms Research Library of the United States Army, whose digital collections are vast, largely free to the public, and incredibly informative.

Nimur (talk) 20:38, 26 November 2016 (UTC)

Firestorm

What weather conditions are optimal for the development of a firestorm (such as after the WW2 carpet-bombing of Hamburg and Dresden)? How often do these weather conditions occur in the Arabian Peninsula? (Or, in lay terms, is it possible to Dresdenize a city like Mecca?) 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 06:33, 20 November 2016 (UTC)

According to our article on Firestorm, the quantity of combustibles per square meter necessary for a firestorm to form is (40 kg/m²), which Mecca almost certainly lacks. --Guy Macon (talk) 07:03, 20 November 2016 (UTC)

Do gas mains (or oil pipelines) count toward this figure? Just askin' ;-) 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 07:37, 21 November 2016 (UTC)

You would want a lack of current rain, at the very least, and dry conditions would be ideal. Also, if some form of visual targeting is used, then a lack of cloud cover is required, and perhaps daylight, or at least strong moonlight, if there aren't any lights to guide the bombers to their target. Of course, modern bombers have many methods of finding a target that don't rely on visual cues. StuRat (talk) 18:43, 20 November 2016 (UTC)

And these are often seen in desert areas (although in the case of Saudi cities, their construction mitigates against it) -- what about upper atmospheric conditions? The WP article mentions a jet stream enhancing firestorm effects, and another source claims that a thermal inversion is important for the development of a firestorm -- is this true (and are there any further fine points like these), and if so, are these conditions often seen on the Arabian peninsula? (BTW, what if the attacking force uses not just bombers but also artillery and rocket launchers?) 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 07:37, 21 November 2016 (UTC)

Feynman Lectures. Lecture 38. Ch. 38–1 Probability wave amplitudes [2]

This means that the idea of a particle is limited. The idea of a particle—its location, its momentum, etc.—which we use so much, is in certain ways unsatisfactory. For instance, if an amplitude to find a particle at different places is given by e^{i(ωt−k⋅r)}, whose absolute square is a constant, that would mean that the probability of finding a particle is the same at all points. That means we do not know where it is—it can be anywhere—there is a great uncertainty in its location.
— Feynman • Leighton • Sands, The Feynman Lectures on Physics, Volume I

Also I have found in [3] that $|\psi |^{2}=\mathrm {const}$.

Besides we know that length of complex number is real coefficient at e^iθ. In this case coefficient = 1.

But I don't understand are t and r constant? Can you show that if momentum is known e^{i(ωt−k⋅r)} = const |e^{i(ωt−k⋅r)}|² = const? And when then e^{i(ωt−k⋅r)} ≠ const |e^{i(ωt−k⋅r)}|²≠ const and we can determine where the particle is? Username160611000000 (talk) 08:57, 20 November 2016 (UTC)

The variables t and r are not constants. They are coordinates - time and position. The probability wave for the position of a particle with a precisely known momentum is e^{i(ωt−k⋅r)}, the probability of finding the particle at any position is proportional to the square of the absolute value of that probability wave and that is 1 - so it has the same probability of being anywhere. It's position is completely unknown. The value of that probability wave is a complex number, it is not a constant, only its absolute value is constant - and that is only because the momentum is known precisely. Dmcq (talk) 11:52, 20 November 2016 (UTC)

Yes, must be |e^{i(ωt−k⋅r)}|² = const.
But then it is always true, because |e^{i(ωt−k⋅r)}|² = 1. Even if k (and so momentum) is not constant, equation is true. To find the particle we must have |e^{i(ωt−k⋅r)}|² = 0 for some r. How is it possible? Username160611000000 (talk) 12:11, 20 November 2016 (UTC)

That being zero would mean there was no chance of finding the particle there. Dmcq (talk) 18:14, 20 November 2016 (UTC)

Zero square of amplitude means zero chance, it's clear. But zero square of amplitude is impossible because |e^{i(ωt−k⋅r)}|² = 1 , always. Or please show how non-constant momentum makes square of amplitude zero in some places and nonzero in other places.Username160611000000 (talk) 18:26, 20 November 2016 (UTC)

Ψ(r,t) = e^{i(ωt−k⋅r)} isn't a physically sensible wave function (because it can't be normalized). It's best to think of it as an unphysical limit of physically sensible functions, much like the Dirac delta function (which is closely related, as it's the Fourier transform of this thing). Physicists like it because it's mathematically simpler than more realistic wave functions, but when you work with it you have to be careful to remember that it's only a limit, not a meaningful object in its own right.

A wave function describing a real particle would square-integrate to 1 and would not have the same value everywhere in R³.

It isn't necessary for the wave function to be zero anywhere for the particle to be "findable". A Gaussian distribution is nowhere zero, but it still makes sense to sample a random value from a Gaussian distribution. It can be arbitrarily far from the center, but usually is pretty close to it. The squared norm of the Dirac delta function is the limit of normalized Gaussians as the standard deviation goes to 0, and the squared norm of the function you're asking about is the limit of normalized Gaussians as the standard deviation goes to ∞. -- BenRG (talk) 22:19, 20 November 2016 (UTC)

Thank you, but I know nothing about the wave functions so far, just the amplitudes in experiment with electrons and two holes. Username160611000000 (talk) 07:47, 21 November 2016 (UTC)

Culmination of constellation's visibility

I noticed there's some mess about when Coma Berenices (and possibly other constellations) is best visible. In case of Coma Berenices and apparently for Northern Hemisphere this book gives "midnight, 2 April", this website says "early May" and this book even gives three months: early March, 2 a.m., early April at midnight and early May at 10 p.m. I suspect it's because of different latitudes, but none of the sources makes such an adjustment which is strange. Which one to choose? Brandmeister^talk 11:26, 20 November 2016 (UTC)

It's because culmination time constantly gets 2 hours earlier every month. Sometimes it's in daytime so no one would pick those months. Among the nighttime culminations midnight (apparent solar time) might win tiebreakers like "highest average nighttime height" edit: and high latitude twilight avoidance (thanks 90.) but usually people American publications that use 40° latitude charts give the month season and maybe culmination date of a constellation as when it culminates in the dark part of the evening. Sagittarian Milky Way (talk) 17:46, 20 November 2016 (UTC)

i.e. In 2016 the center of the northern winter constellations culminate at midnight around the December solstice but the center of winter is after the solstice so in the coldest part of the year that point culminates in the evening. Sagittarian Milky Way (talk) 19:03, 20 November 2016 (UTC)

[Edit Conflict] The latitude makes no difference, as the constellation will still culminate (at which point it will be highest in the sky) at the same time on the same date regardless of its elevation.

Note that the three answers are not contradictory, the first gives the date (April 2nd) for culmination at true midnight (minimising any residual twilight from the set Sun, which can be significant at higher latitudes) the second for culmination at daylight-saving 11:00pm, and the third gives dates for culminations at three different (true) times depending on how late you want to be awake (later times may reduce interference from artificial lighting). {The poster formerly known as 87.81.230.195} 90.208.174.251 (talk) 17:57, 20 November 2016 (UTC)

This would not matter much in Brooklyn or Las Vegas. The astronomical magnitude scale shows the eye isn't sensitive to smallish brightness changes and cars and peoples' windows are not a big part of the evening skyglow when there are that many streetlights and signs that never turn off. There's parts of the suburbs without streetlights so how many headlights and rooms in the area are lit is more likely to be significant there. Sagittarian Milky Way (talk) 19:12, 20 November 2016 (UTC)

Uncoupling agents as a hypothermia countermeasure?

Given that hypothermia results from heat loss that outstrips the body's rate of thermogenesis, and that the main effect of uncoupling agents like 2,4-Dinitrophenol is to greatly increase the rate of thermogenesis to far above its normal range, could 2,4-DNP and\or other uncouplers be useful in counteracting severe hypothermia? It seems to me, at first glance, that this would be a very useful tool for first responders in areas with cold winters, as well as for people with occupations and\or hobbies placing them at a high risk of getting severe hypothermia (the examples I had in mind were cold-water fishermen and high-altitude mountaineers, specifically, but there'd also be lots of others)... so, then, how come this isn't (so far as I know) a thing? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 14:16, 20 November 2016 (UTC)

As an aside: A retired Jewish Doctor told me some years ago that she was disgusted that a French pharmaceutical company was promoting Chlorpromazine as an aid to hypothermic surgery without mentioning nor acknowledging they were using data which was gained by the Nazi's during their experiments in concentration camps. Apparently, downed aircrew where often retrieve alive from the cold seas only to die soon after from the latent effects of hypothermia. So the Nazi doctors came to focused on an insecticide used for intestinal parasites . Its action was to make the parasites lose grip on the gut wall, enabling the normal peristaltic motion of the gut to flush them out. Ie. It did not kill them it just paralysed them. It was observed that concentration camp inmates so treated, showed more indifference to the cold and so were experimented upon further to aid the survival of downed airman. Many inmates died during those experiments from immersion in ice cold water. Having done voluntary work in a psychiatric hospital I have witnessed this indifference to the cold for myself and thus was given the harrowing history (which was far more detailed and graphic to the little I have mentioned) . Yet the pharmaceutical company declared that it was its own discovery. Think about it. Without this data, who would have thought that hypothermic surgery could be performed by injecting the patent with a insecticide? Yet they never made mention of the source. Given her personal and family experiences and the pharmaceutical company's desire to distance itself from negative connotations I can sympathize with her grievance. All expression left her face as she recounted these thing. It was as if there was no way that she could speak and feel emotion at the same time. It was just voiced cold and matter of factually.--Aspro (talk) 17:52, 20 November 2016 (UTC)

Sounds like Nazi human experimentation#Freezing experiments should mention this rewarming method (with cite obviously). DMacks (talk) 03:14, 22 November 2016 (UTC)

Oh wait, sounds like they were just using the hypothermia data (which is noted at Nazi human experimentation#Modern ethical issues), not chlorpromazine as a treatment. That would be a chronological problem, and also I can't this or other drugs listed as http://remember.org/educate/medexp or similar resources. DMacks (talk) 03:27, 22 November 2016 (UTC)

Chlorpromazine was a 1930's medication. There is no chronological problem other than that created by the pharmaceutical company not disclosing the full history. Chlorpromazine reduces the instinct to shiver. Shivering uses up the available glucoses and it takes time for the liver to start utilizing glycogen (a gross over simplification on my part). Thus, some downed air men were recover from the sea, very cold but still alive, but as they warmed up, their blood pressure, suddenly and dramatical fell -causing death due to their bodily resources having been depleted... What 1950's surgeon or anaesthetist would contemplate cooling a surgical patent down to such low temperatures and then inject them with an insecticide? All without doing any prior experiments before hand? Unless of course they had prior knowledge. Leave it to your common sense to realize that some information is widely available and some peoples personal recollections fill in the missing gaps. Together, they make the whole.--Aspro (talk) 19:02, 22 November 2016 (UTC)

I'm not really sure where you're going with this. Sure, information can be traced back to these atrocities at concentration camps. Modern cancer treatment with alkylating agents owes a debt to the air raid on Bari and the mustard gas the Allied ship was carrying just-in-case. People taking lisinopril for high blood pressure should thank the folks bitten by jararacas for demonstrating what the venom did to their blood pressure. Bad things happen, and people learn from them. Wnt (talk) 20:07, 22 November 2016 (UTC)

According to our Chlorpromazine article, "Chlorpromazine was discovered in 1950" with two cites (though one actually says 1951). User:Aspro, do you have a ref for it being known in the 1930s? DMacks (talk) 20:29, 22 November 2016 (UTC)

@ DMacks. I'm becoming aware that as the decades pass my brain becomes ever more ossified. So since you asked a sensible question about chronology, I thought it was only fair to re-check those recollection of which I was told (which I followed up back-then, to satisfy my curiosity). Chlorpromazine is a slightly modified form of phenothiazine (just stuck chlorine atom on it and hey-presto a new patentable drug) (drugs that have names like Flupentixol [flu] have fluorine atoms added and hey presto more new patenable drugs etc.). As such, it allowed the pharmaceutical company to patten it as its own and receive billions in royalties but its effect were the same (found at the same time, Thalidomide was also a Nazi era drug and is documented). As you may know, the German chemical industry did a lot of work also on organochlorine compounds – they were thought important for chemical warfare and there is a strong suggestion that the molecule that was later known as chlorpromazine was in existence and used before the end of the war. Didn't think that I would ever need to reference this information ever again. It was just to satisfy my own curiosity so made no note of it. Now, I wish I had and I wish I had taped the recording of what was recounted. A quick search in my med library uncovered Robert Whitaker's book: Mad in America: Bad Science, Bad Medicine, and the Enduring Mistreatment of the Mentally. Chapter 6 page 142 and some other pages also allude to bad science concerning the 1930's use of phenothiazine as an insecticide and the later marketing of chlorpromazine. Hope this helps in some small way.--Aspro (talk) 21:50, 23 November 2016 (UTC)

The article you yourself linked to says under Health Effects:

"DNP is considered to have high acute toxicity. Acute oral exposure to DNP has resulted in increased basal metabolic rate, nausea, vomiting, sweating, dizziness, headache, and loss of weight. Chronic oral exposure to DNP can lead to the formation of cataracts and skin lesions and has caused effects on the bone marrow, central nervous system, and cardiovascular system."

Elsewhere it mentions the frequent fatalities associated with its illicit use. So, long story short, if you used it to treat hypothermia you'd likely kill the patient with it, and if you used it prophylactically for persons routinely exposed to cold you'd likely injure or kill them with longer-term side effects. There are much less dangerous answers to both problems.

That's not to say that further research might reveal ways to use it more safely for the purposes you suggest, but good luck with designing ethically acceptable means of testing such uses and getting them funded. {The poster formerly known as 87.81.230.195} 90.208.174.251 (talk) 18:13, 20 November 2016 (UTC)

The article also says that the main cause of the acute effects is the increase in thermogenesis:

"The factor that limits ever-increasing doses of DNP is not a lack of ATP energy production, but rather an excessive rise in body temperature due to the heat produced during uncoupling. Accordingly, DNP overdose will cause fatal hyperthermia, with body temperature rising to as high as 44 °C (111 °F) shortly before death. In light of this, when it was used clinically, the dose was slowly titrated according to personal tolerance, which varies greatly."

Which would be much less harmful if the person was starting out from a moderately to severely subnormal core temperature. If you're at normal (~37C) body temperature, then raising your core temperature by 7C is likely to kill you. If, on the other hand, you're moderately hypothermic (let's say 30C CBT), then raising your core temperature by 7C will merely bring you up to normal temperature.

Secondly, I never suggested using it prophylactically—merely having an uncoupler on hand to use in case one gets severely hypothermic. It's (or would be) kind of like an Epi-Pen in that regard. One doesn't prophylactically use one's Epi-Pen on oneself beforehand—one merely keeps it (relatively) handy in case they get exposed to the allergen their reaction to which necessitates the Epi-Pen.

Thirdly, if one is currently in the process of freezing to death, wouldn't worrying about possibly getting cataracts and whatnot in the longer term be rather low on one's list of priorities relative to not freezing to death right now?

And, fourthly, I don't believe I suggested that 2,4-DNP was necessarily the uncoupler of choice anyway—I was more using it as an example of an uncoupler. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 21:37, 20 November 2016 (UTC)

No drugs needed. Count Iblis (talk) 03:52, 21 November 2016 (UTC)

Video content is some kind of water torture. Just go to tummo and get the relevant information right away (at least, if you scroll down to near the end where the data is). Wnt (talk) 20:13, 22 November 2016 (UTC)

Wim Hof gives courses on this method. I guess if you do regular hyperventilation exercises you train the body to burn more energy when you breathe fast, the hyperventilation becomes normal ventilation because the body simply revs up the metabolic rate. Count Iblis (talk) 07:37, 23 November 2016 (UTC)

The problem with DNP in particular is that it is just too effective at what it does (uncoupling oxidative phosphorylation). The therapeutic index is way too small and even supposedly "safe" doses for one person may end up killing another person. You may want to try a less effective uncoupler, preferably one without this many side effects (e.g. cataracts, and things resulting from intracellular Ca²⁺ levels rising unchecked). As for the idea itself, this is more biology than chemistry, so I'll wait for someone more competent in that field to weigh in. Double sharp (talk) 05:18, 23 November 2016 (UTC)

This strikes me as an interesting idea. Ultimately, this is biology, and biology doesn't know theory. Either we find an existing experiment that addresses this idea, or else we have to wait until one is done to know what would happen. A bit of a warning flag here is that hypothermia treatment sometimes focuses on not raising body temperature too quickly, and we'd have to look at the specific pattern of heating from the uncoupling agent. Wnt (talk) 13:36, 23 November 2016 (UTC)

The wasting from energy as heat from DNP (ah, this is the chemistry I can comment on) is from cellular respiration and ATP production, so I presume it would start from the mitochondria. Double sharp (talk) 15:40, 24 November 2016 (UTC)

I was thinking more of, oh, pharmacokinetics and related issues. For example, how much is absorbed in portal circulation before reaching the rest of the body, whether there are differences in cell permeability to the compound depending on cell type, effect of CYP450s or other detoxification enzymes ... I don't know, honestly I haven't even looked this up because I doubt a lot of work has been done in humans in recent years, and the older work, even if it covered such issues, would be harder (though certainly possible) to access. I'd want to see empirical data, at very least a FLIR image of someone dosed with the drug; I looked for it and found [4] which just says DNP is not used any more, despite obvious interest (I imagine getting the experiment past an institutional review board would be interesting). Maybe something could be found for some more recent drug, like MDMA, which the evacuees might like better anyway. :) wait no, that apparently affects heat dissipation, which isn't an issue in hyperthermia. But it didn't come up in a simple MDMA FLIR PubMed search. Wnt (talk) 21:22, 24 November 2016 (UTC)

It wasn't just the Nazis. When the Japanese occupied Harbin they put prisoners outside naked in winter overnight and watched to see what would happen. See Unit 731. 86.145.54.170 (talk) 14:04, 26 November 2016 (UTC)

High voltages, low currents, and Ohm's law, oh my!

One often hears people talking about how some electrical discharges and circuits (such as lightning, electrostatic discharge in computer components, electric fences, etc.,) can have incredibly high voltages but nevertheless don't (usually) kill people, and this being supposedly a result of these power sources producing really high voltages but really low currents. My question is this: how can this be possible, given that Ohm's law states that, in all cases, $V=IR$, and, therefore, for a given voltage (holding $V$ constant) applied across a given object (meaning, at least at first, that the resistance—$R$—is being held constant), one should always get the same current flowing through the object, no matter its source? According to Ohm, shouldn't a (supposedly) 500-volt electrostatic discharge be considerably more lethal than 120- or 240-volt household wiring, and almost as deadly as stepping on a live third rail (generally 600 or 625 volts in the US)? So why, then, is it that no-one ever hears about unwary ITs being fried by errant ESD—are the huge-voltage-tiny-current claims false, or is it Ohm's law that's wrong? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 14:54, 20 November 2016 (UTC)

The very high voltage only exists for a very tiny moment. Real voltage sources are not ideal voltage sources. For most static electricity situations, the total capacity is low, so as soon as current is flowing, the charges equalise and the voltage (and with it the current) breaks down. The total energy ($\int I(t)U(t)dt$) of such a discharge is therefore quite low. --Stephan Schulz (talk) 15:14, 20 November 2016 (UTC)

Ah, thanx—that makes sense. (That still leaves the electric fences, but I'm guessing that the source in that case [of the information, not the voltage! X-P] was probably just wrong\misinformed.) Whoop whoop pull up ^{Bitching Betty | Averted crashes} 15:30, 20 November 2016 (UTC)

Very similar question: one often hears that a step-up transformer is able to increase the voltage in its output loop beyond that in its feed loop because it decreases the current in the output loop to compensate (and the reverse for a step-down transformer), and that this lower current means less loss en route to distant customers, which is supposedly why we use step-up transformers and humongous transmission voltages (our very own article [!] on Electric power transmission makes this claim, as does Railway electrification system)—but, according to Ohm's law, voltage and current are directly proportional, not inversely proportional! So, since $V=IR$, shouldn't increasing the voltage in the output loop also increase the current in step with the increase in voltage, not decrease it? Is the resistance in the output loop somehow massively greater than in the feed loop, so as to satisfy $V=IR$ and allow a low current even with an enormous voltage? Did Ohm have his head screwed on wrong? Or is it all our modern electrical engineers who have it back to front? Or something else entirely?

Utterly perplexed... Whoop whoop pull up ^{Bitching Betty | Averted crashes} 14:54, 20 November 2016 (UTC)

The thing to realize is that power is a constant, i.e., $P=VI$= constant. (Otherwise we could magically create energy by putting our power source through one transformer after another.) So for a given P, if V goes up I has to go down and vice versa. Shock Brigade Harvester Boris (talk) 17:21, 20 November 2016 (UTC)

I think the key point you're missing is that Ohm's law is not a universal law of electricity. It only applies to (ideal) resistors. Transformers are nothing like ideal resistors, and don't obey Ohm's law. (Transformers have internal resistance, but a transformer as a whole is not like a single resistor with a single value of R.) -- BenRG (talk) 21:41, 20 November 2016 (UTC)

A good way of looking at it is internal resistance. It's the reason why you can get a nasty shock from a 12v car battery; but at the same time get unhurt from many thousands of volts, like a high voltage generator we had at my old physics lab. Sources with high internal resistance can be harmless even at many thousands of volts, while sources with low internal resistance can give you a nasty shock at a few volts. --Jules (Mrjulesd) 18:07, 20 November 2016 (UTC)

It is neither the voltage nor current but the total energy which is of prime importance. We have an article Earth leakage circuit breaker but even that does not explain it in my view. Even Electrocution doesn't seem to point out that it is the complete depolarization of the cells that stops them from functioning. These articles need expanding. Edison tried to use this as his USP in so much that his DC system didn’t depolarized the same as AC did. --Aspro (talk) 18:13, 20 November 2016 (UTC)

Power really rather than energy. However the concept of internal resistance is useful in explaining why voltage sources differ from a pragmatic angle.--Jules (Mrjulesd) 18:22, 20 November 2016 (UTC)

Power is the 'rate' of doing work which is the wrong unit. I'm talking about energy. --Aspro (talk) 20:05, 20 November 2016 (UTC)

• Others mentioned transitory effects because of the way it was formulated, but I suspect Whoop whoop pull up's original confusion was much simpler than that.

Consider a spark plug powered by a car's battery, which we can model as an ideal DC voltage generator of 24V. During a spark, current is fairly low, because it has to go through air which has a huge electric resistance. However, if you wire yourself to the battery (need I say not to do this?), you have quite a lower electric resistance. Consequently, assuming the battery generates the same voltage, the current is higher, hence the expended power is higher as well (and, as explained above, power is what really matters). Even though $V=IR$ could reasonably be applied in both cases, $R$ is not the same for the various "resistances" (air, human) considered. Tigraan^{Click here to contact me} 22:36, 20 November 2016 (UTC)

There's one point we should clarify here - the voltage across a spark plug is around 25 kV. It's generated by the ignition coil, not directly from the battery - see ignition system. Car batteries are dangerous in many respects, but don't pose a risk of electric shock. You should indeed avoid touching the HT leads in a car, but the battery terminals won't hurt you. Tevildo (talk) 07:23, 21 November 2016 (UTC)

OK, so my example was a terrible one on multiple accounts. Sorry. Tigraan^{Click here to contact me} 17:40, 21 November 2016 (UTC)

Ohm's law states that V and I are proportional (or equivalently that V/I is constant) in a conductor to which it applies, such as an ideal Resistor component. But it is not a conservation law for transformers! The quantity that an ideal power transformer conserves is Electric power $P$ given by

$P=VI\,$

A utility power transformer does not alone decide the power that it delivers to customers; that depends on the sum of the currents that they individually draw. The power generator "sees" a load whose effective resistance is (resistances of all customer equipments in parallel ^{see ref.}) x (overall step-down voltage ratio from generator to customers).

Electric fences usually emit only short pulses of high voltage from a source that has high internal resistance and low capacity. This ensures a low-energy non-lethal discharge, extends battery life and avoids starting fires in dry foliage. DaDoRonRon (talk) 00:40, 21 November 2016 (UTC)

I suppose that part of it is that nature doesn't dish out voltages that often; more often it dishes out currents: for example, the transfer of surface charges in the case of static electricity requires a certain amount of charge to move to balance the equation. But the path for that charge to move via spark is very high in resistance, so the voltage that accumulates before the spark starts is very high. Part of it also is that capacitance in many unplanned situations is very low; a foot with a sock on it is not really designed to power a TV set. :) This means that very high voltage can build up before much charge is accumulated. Wnt (talk) 03:33, 21 November 2016 (UTC)

• One significant correction to the original question: lightning very frequently does kill people. --76.71.5.45 (talk) 09:29, 21 November 2016 (UTC)

... because the large capacitance means that currents can be high as well as voltages. Dbfirs 14:18, 21 November 2016 (UTC)

Hence the "usually" qualifier in my original question (because lighting victims do usually—70% to 90% of the time—survive). Whoop whoop pull up ^{Bitching Betty | Averted crashes} 15:45, 23 November 2016 (UTC)

Well, that's a case in which, as I put it, a voltage is dished out: the charge builds up until the lightning can cross the gap between cloud and ground. I didn't want to get into calculating the capacitance of a thundercloud just now, but these folks think it is in the nanofarads, which is pretty impressive for a natural system but still not very high compared to electronics parts. Wnt (talk) 12:34, 22 November 2016 (UTC)