Wikipedia:Reference desk/Archives/Science/2017 May 24

= May 24 =

Decentralized electric networks
Are electric networks of low volts always being decentralized?--109.252.29.219 (talk) 11:00, 24 May 2017 (UTC)
 * Can low volts to create centralized electric networks?--109.252.29.219 (talk) 11:07, 24 May 2017 (UTC)
 * I think you're asking if there are any large scale low voltage networks. See Electric power transmission. Not at the moment - energy is saved by transmitting electricity at a high voltage. The voltage is stepped up at the generators and stepped down using transformers near the point of use. So high voltage AC is how electricity is transmitted nowadays. High-voltage direct current is also used for some long distance links. There are plans I believe though to transmit power using low voltage DC in superconducting networks. This sort of thing would be a very large project for sending power between countries for instance. Dmcq (talk) 11:12, 24 May 2017 (UTC)
 * Thanks a lot. Are low volts of renewable energy not powerful to create centralized electric networks?--109.252.29.219 (talk) 12:23, 24 May 2017 (UTC)
 * Are being plans to use optical resonance in optical fiber to transfer electricity of low volts for long distances?--109.252.29.219 (talk) 12:36, 24 May 2017 (UTC)
 * Volts is not the same as power or energy. A meal for instance gives a certain amount of energy. A person cycling has a maximum amount of power they can produce per hour and using the energy in one meal could probably produce it for a few hours. The gears on his bicycle produce either high speed with low force or low speed with high force. A transformer is like that - it can produce high voltage electricity with a low current or a low voltage with a high current for the same power.
 * Renewable energy is not a particular amount of energy. An installation producing renewable energy could be large or small. If it is small it produces only a small amount of power and if it is large it produces a lot. A transformer can transform the voltage and does not care what the source is.
 * No there are no plans to send power down optical cables. Why should anyone try to do that when there are perfectly good electricity power lines around? Dmcq (talk) 13:03, 24 May 2017 (UTC)
 * There are a few cases where it is useful to transmit power by Optical fiber using a photovoltaic cell to convert the light into electricity. While inefficient, it is a way to avoid having a metallic conductor near MRI machines, which produce strong magnetic fields. Other examples are for powering electronics in high-powered antenna elements and measurement devices used in high-voltage transmission equipment. Blooteuth (talk) 16:34, 24 May 2017 (UTC)

Is it true that low volts always carry low power and low Ampere’s force?--109.252.29.219 (talk) 14:18, 24 May 2017 (UTC)
 * Because the low dynamics - low kinetics will not be high dynamics, isn't it?--109.252.29.219 (talk) 14:29, 24 May 2017 (UTC)
 * As for me the volts and the Ampere's force are always directly proportional to the power.--109.252.29.219 (talk) 14:50, 24 May 2017 (UTC)
 * Agree that the potential kinetics of power cannot be more potential kinetics of volts or potential kinetics of Ampere’s force.--109.252.29.219 (talk) 16:11, 24 May 2017 (UTC)
 * Is it true...? No. Electric power is the product of Voltage and current which are separate, measurable variables. The supply for an electric arc welder is an example of a low voltage producing a very high current, and therefore delivering a high power. The Weller Soldering gun also delivers substantial heating power using a low-voltage high-current transformer winding. Blooteuth (talk) 16:48, 24 May 2017 (UTC)
 * Much thanks. The kinetics of power always closer to the kinetics of volts or kinetics of Ampere’s force?--109.252.29.219 (talk) 18:37, 24 May 2017 (UTC)
 * Please read the first 3 articles that I linked to in my answer. It is not necessary to learn Ampère's force law to understand electric power, voltage and current. Blooteuth (talk) 21:39, 24 May 2017 (UTC)
 * The lower the voltage is, the higher is the current for same energy transfer. This increases lost on conductors and connectors. High current needs thick wires. This means more conductive material is needed. Taking a closer look inside a computer, modern CPUs have operating voltages far below two volts. The buck converter, generating this low voltage for the 12 volts power supply is located on the motherboard due voltage drop on connectors and lines. When the CPU operating voltage drop at any time, the CPU goes into brownout, causing malfunction and discontinuing the program flow. Cheaper and older computer failures are caused by this. Starting the engine of a car, the 12 volts from battery are not 12 volts anymore when the starter motor drives the engine. Lower light from bulbs appear at this time. Using a bigger battery helps a litte, but the lead in the starter battery is no super conductor. An other example is, increasing the length of wires computer power supplies by plugging a number of Y-cables or Y-adapters can increase the resistance of the wires to the point, where shortcuts are not detected anymore, causing burning the wires and starting a fire. In the Low Voltage Directive, also taken most likely for American standards, prevention of similar damages are regulated. There are technologies like smart grid and high-voltage direct current, to interconnect low(er) voltage power grids. -- Hans Haase (有问题吗) 09:32, 25 May 2017 (UTC)

Thank you. According to the Law of conservation of energy, the low dynamics - low kinetics will not be high dynamics – high kinetics.--109.252.29.219 (talk) 09:35, 25 May 2017 (UTC)

Electric field at plane of non-conducting uniformly charged thin disk
Will field at plane of a disk excluding the disk itself be zero? Here basis of above conclusion is that the field lines will originate perpendicularly to the plane, and from both faces therefore they will never be able to reach plane of disk at finite distance.

From above the potential at edge will also be zero, if a test charge is bought from infinity through the path passing through plane to the edge, which is obviously not true.

Therefore, tell me where I'm wrong and please provide the field line distribution due to the disk. — Preceding unsigned comment added by Tejasvi Singh Tomar (talk • contribs) 14:22, 24 May 2017 (UTC)
 * An Electric field is a vector field that associates to each point in space the Coulomb force that would be experienced per unit of electric charge, by an infinitesimal test charge at that point. Let's distinguish between these cases.

 + +  +  +  +  +                 +  +  +  +  +  +    + OOOOOOOOOOOOOOOO +               OOOOOOOOOOOOOOOO + +  +  +  +  +                 -  -  -  -  -  -

CASE "A"                         CASE "B"
 * Case A is a uniformly charged disk which may be conductor or insulator. Electric field lines emanate to infinity from every "+" point including the edge. The density of the lines correlates with the strength of the force. At a large distance their density is the same so the force is the same for a point in the plane of the disk as any other. One may also sketch the shapes of Equipotential surfaces which in 2-D are sausage-shaped close to the disk and circular far from the disk.


 * Case B is a differentially charged insulator disk. Electric field lines emanate from every "+" point then bend towards and pass through the plane of the disk at 90 degrees, then continue bending to meet the "-" on the other side. There is an equipotential surface of zero potential throughout the plane of the disk so in this case it is true that no work is needed to bring a charge from infinity to the edge of the disk. Blooteuth (talk) 16:21, 24 May 2017 (UTC)
 * If the disk is finite, the answer is no. The field in the plane of the disk will not be zero and the field lines in the plane will be parallel to it. Ruslik_ Zero 14:43, 25 May 2017 (UTC)

Table salt
Are all table salts made of sodium chloride? Or is sodium chloride the principal ingredient, mixed with other compounds for nutrition, either naturally or artificially? If hydrochloric acid and sodium hydroxide make water and table salt, then can that be placed in soup and still be safe to drink? 140.254.70.33 (talk) 16:54, 24 May 2017 (UTC)
 * From Salt: Salt is used in many cuisines around the world, and is often found in salt shakers on diners' eating tables for their personal use on food. Salt is also an ingredient in many manufactured foodstuffs. Table salt is a refined salt containing about 97 to 99 percent sodium chloride.[35][36][37] Usually, anticaking agents such as sodium aluminosilicate or magnesium carbonate are added to make it free-flowing. Iodized salt, containing potassium iodide, is widely available. Additional info follows regarding more specialized salts such as fortified (which has various other additives), sea salt (which contains other salts), Himalayan salt (which has additional content), etc. Iapetus (talk) 17:13, 24 May 2017 (UTC)
 * [Edit Conflict] Searching for Table salt on Wikipedia would have redirected you to Salt, which should mostly answer your first two questions.
 * I will leave the last question for others with greater chemical knowledge to address (with the caveat that the formulae described in introductory chemistry textbooks are often idealised, and ignore all sorts of minor side reactions that can produce other products in lesser quantities). I would ask, however, why anyone would want to go to the additional bother of obtaining these reagents and performing the reaction, as table salt itself is in the modern world plentifully available and cheap? {The poster formerly known as 87.81.230.195} 2.122.60.183 (talk) 17:15, 24 May 2017 (UTC)
 * Chemical equations suggest that the equations go back and forth. But that depends on the speed of the reverse reaction. HCl and NaOH are both strong acid and base, respectively. So, they are supposed to dissolve completely. In that case, the H+ and OH- will bind and may form more water molecules. And the Na+ and Cl- will bind and may form salt, which dissolves in water. I wonder if the finished product will taste like salt water. 140.254.70.33 (talk) 17:32, 24 May 2017 (UTC)
 * You'd better be damned sure you're exact on your amounts. If you're off by 1 part in a thousand in either direction, your solution will taste shockingly sour or soapy.  The behavior of a neutralization reaction is quite sensitive near the equivalence point.  -- Jayron 32 17:35, 24 May 2017 (UTC)
 * Will adding a buffer help? What kind of buffer is non-toxic? Can one use pig blood purchased from a grocery store? 140.254.70.33 (talk) 17:55, 24 May 2017 (UTC)
 * If you're making black pudding. -- Jayron 32 19:58, 24 May 2017 (UTC)
 * Also, while you can make NaCl + H2O from HCl and NaOH, you'd better premix it outside your soup, otherwise either or both reagents will react with soup stuff (tm) causing probably undesirable results. But we did the basic experiment in chemistry class - you use a titration pipette and a indicator strip to get close to neutral. Our teacher made us taste the result (salty, as expected). But he also had us make nitroglycerin and managed to put a permanent stain on the ceiling of the lab with a piece of metallic potassium causing an unexpectedly vigorous reaction. And we got to distill (bad) wine into (worse) brandy, with surprisingly low yield... --Stephan Schulz (talk) 17:51, 24 May 2017 (UTC)
 * The proposed in-soup reaction is
 * HCl(aq) + Na(OH)(aq) → H2O + NaCl(aq)
 * In this reaction both the sodium and chloride ions are spectators as the neutralization reaction,
 * H+ + OH− → H2O
 * does not involve them, but since it is exothermic it will help keep the soup warm. Blooteuth (talk) 19:28, 24 May 2017 (UTC)
 * I wouldn't try it unless you knew that your starting chemicals were food grade. Industrial chemicals can have some nasty impurities. shoy (reactions) 19:26, 24 May 2017 (UTC)


 * Table salt consisting of mainly potassium salts also exists. But note that salt in the way we use it is poisonous, had we not used salt since thousands of years then the FDA would never have approved its use in foods, not even a fraction of a gram of it. It would only have been used as drug to deal with water poisoning and perhaps some complications due to using diuretics. Count Iblis (talk) 22:25, 24 May 2017 (UTC)


 * I think deer are known to lick the underwear of unsuspecting campers for salt content. I think some animals lick rocks for salt. Are you suggesting that humans should lick rocks for salt? Or are you suggesting that humans should get sodium elsewhere - celery or pig's blood? 140.254.70.33 (talk) 22:42, 24 May 2017 (UTC)


 * Iblis has idiosyncratic beliefs about diet and nutrition, which he will gladly attempt to "prove" by cherry-picking source (mostly pseudoscience) to prove. You can safely ignore anything he has to say on the matter, and instead refer to well established sources.  -- Jayron 32 22:44, 24 May 2017 (UTC)


 * We do need a fair amount of salt. That could come from seafood, or we can add salt to other foods.  This is a reasonable thing to do, so long as we keep the amounts reasonable.  For a rough rule-of-thumb, the average person needs about 2000-2500 mg of sodium a day (there's debate on this, but this is the figure I will use) and about that many kilocalories, so foods should have roughly the same mg of sodium as kcals.  Some may be a bit more, some a bit less, but if most of your food has many times as many mg of sodium as kcals, then that's too much. StuRat (talk) 23:04, 24 May 2017 (UTC)
 * That 2000-2500 mg is the upper limit above which you can already easily detect symptoms in healthy people, the recommendation is to not go above that, but somehow this has become a proxy for the RDA. Count Iblis (talk) 23:31, 24 May 2017 (UTC)


 * I cited a well established source (International journal of epidemiology published by Oxford Academic). So, while we do need salt, it's just about 50 milligrams per day even if you sweat a lot (if you only get 50 mg of salt a day your sweat won't contain much salt anymore). Animals in the wild have to do with what they can eat in the wild, and they may from time get a bit short on salt. These animals typically weigh a lot more than we do and they have not added any table salt in their food since they were born. The consequences of the "normal" amount of salt in our diet is that instead of a blood pressure of 100/60 that most Yanomami Indians have, we have blood pressures of 120/80 and instead of sticking to 100/60 well into old age like the Yanomami Indians do, the systolic blood pressure rises to 140, 160 and doctors will say that this is just the normal increase due to old age, leading to the "normal" consequences like heart attacks and strokes.
 * The recommendations by the IoM take into account the fact that it's difficult to give up bad habits, they make that explicitly clear and come up with advice on how to reduce salt intake. But you can't take such high end advice as a substitute for the hard facts in the scientific literature. It's similar to the difference between what was known about smoking in the late 19th century and the medical advice at that time,
 * see here: "In the mid- to late-19th century, doctors determined that lip and tongue cancer rates were higher among smokers of pipes and cigars. Despite this link, major medical journals mocked those who opposed smoking. The Lancet, the leading journal of the time and still one of the most important medical journals in the world, wrote in 1879, “We have no sympathy with prejudices against … tobacco, used under proper restriction as to the time and amount of the consumption. ... A cigar when the mood and the circumstances are propitious [is] not only to be tolerated, but approved.” Moderation, not abstinence, was the order of the day." Count Iblis (talk) 23:18, 24 May 2017 (UTC)
 * I have to agree that the FDA, given the chance today, would not approve salt. The hip culinary crowd would make backyard stills to produce tasty illicit meat jerkies.  Elite police squads would be formed to sniff these out with dogs, and the producers would start smuggling bags of the white powder.  On TV you would read about multimillion dollar salt busts as cops stood proudly over the bags of captured material.  Certain desert areas would be fenced off and mined, sea coasts would be wastelands patrolled by thugs with guns defending their turf from rival gangs.  Occasional resorts for rich people, standing out among the crime, would feature kids swimming in the ocean, but if watchful lifeguards caught them swallowing they would get hauled off to jail for five years at a time.  Meanwhile the TV shows would glorify the lifestyle of the salt eater and the massive cartels, with big stakes in the studios, would ensure that a salt cartel never really is defeated in any action movie, and whoever gets tempted to rob their precious white resources would always be suitably punished.  None of this is even slightly more insane than the world we know. [User:Wnt|Wnt]] (talk) 11:30, 25 May 2017 (UTC)
 * @Wnt Condiment on a good story. Blooteuth (talk) 17:20, 25 May 2017 (UTC)
 * Oh, no, that's not the same thing. The situation in colonial India, pre-Gandhi, is what you get after the progressive "legalize, regulate, tax [and monopolize]" crowd finally, after many decades, realize their dream... Wnt (talk) 23:39, 25 May 2017 (UTC)
 * But given that it's allowed, a better strategy may be to create an anti-salt movement like the anti-gluten, anti-GM etc. movements. Count Iblis (talk) 00:27, 26 May 2017 (UTC)

does tb has cure?
does tb has cure? — Preceding unsigned comment added by 31.4.137.4 (talk) 21:00, 24 May 2017 (UTC)


 * If you mean Tuberculosis, then no. Mycobacterium tuberculosis is constantly evolving. There are Multiple-Drug Resistant Tuberculosis, as well as XDR Tuberculosis (extreme drug resistance). There is prevention, though. 140.254.70.33 (talk) 21:09, 24 May 2017 (UTC)


 * ( edit conflict )
 * Tuberculosis is typically treated with a combination of antibiotics. However, this does not necessarily cure the disease as it tends to be very resistant to antibiotics.
 * See Tuberculosis for more information.
 * ApLundell (talk) 21:11, 24 May 2017 (UTC)
 * There is also TB vaccine for prevention. 140.254.70.33 (talk) 21:21, 24 May 2017 (UTC)


 * The pessimism here seems exaggerated. While some very low cure rates have been cited, apparently considering everyone who is given a couple of pills, DOTS (Directly Observed Treatment, Short-Course) has been found to work roughly 60% of the time.  Note that a Cochrane review  finds that the cure rate for people taking pills on their own is not actually significantly lower than that.  And of course the failure of a single short-course treatment with a certain set of drugs doesn't guarantee that some other existing treatment won't kill the mycobacteria.  Really, there aren't many bacterial infections where a course of antibiotics is guaranteed to work. Wnt (talk) 11:18, 25 May 2017 (UTC)