Wikipedia:Reference desk/Archives/Science/2017 July 15

= July 15 =

What happens when the current is too strong for the electrode to measure?
Don't direct me to electrochemistry. Its scope is way too broad and does not answer why I'm not supposed to use an electrode to measure an extremely high current. How will the strong current break the electrode? Is it like a rushing stream and a stick that measures the force of the stream, but if the force is too great, then the stick will break? 50.4.236.254 (talk) 01:25, 15 July 2017 (UTC)
 * Sorry, but it isn't clear what you are asking. There are many types of electrodes.  Pretty much all of them have some sort of limit on the current they can handle, but the specific reasons vary.  It would be very helpful if you could clarify what sort of electrode you are referring to. Looie496 (talk) 03:10, 15 July 2017 (UTC)
 * It's likely due to deviation from ideality. An ideal multimeter should have a linear, or at least polynomial, response, but at high enough current, there's going to be a complex relationship between resistance and heat which probably bring some calculus into the situation which a standard multimeter probe probably doesn't take into account.  That's the best of what I can interpret from the vagueries of the question.  -- Jayron 32 05:33, 15 July 2017 (UTC)
 * I posit this to be about why a multimeter cannot be used to measure high current. The key idea here is that a multimeter does not need to pass much (theoretically, not any) current through it to measure voltage, but the only way it can measure current is to be wired into the circuit and have the entire current pass through it.  This cannot be done reliably past a certain point because it only has so much conductivity, i.e. its resistance can only be so low.  Because V=IR, high current with a nonzero resistance implies voltage builds up across the multimeter, which perturbs the circuit being measured in an unpredictable way making the measurement invalid.  And of course eventually the power dissipation I^2 R means that the multimeter would catch on fire if a fuse didn't stop it first.  That said, you could have some other kind of measuring device that determines the current flow from the magnetic field no matter how strong the current is.  I'm not an expert and have no idea if this is commercially available, or how well it can image the current from careful distributed measurements of the magnetic field and computation.  I suspect that SQUID devices might be used this way from great distances for military purposes? Wnt (talk) 12:30, 15 July 2017 (UTC)


 * The reason I was so reluctant to answer is that the OP referred to electrochemistry, where specialized electrodes are used to measure the concentrations of chemicals. The factors that come into play there are quite different from those that come into play when ordinary metal electrodes are used to measure voltages. Looie496 (talk) 23:22, 15 July 2017 (UTC)


 * The Hydraulic analogy (see article) is useful in understanding basic electronics but "poking a stick in a stream" is not the way to apply it. One attaches an Electrode to a system either A) to apply or extract electricity, or B) to measure what is happening in the system. In the field of electrochemistry, A) might apply to electrolysis or a battery and B) to the measurement of cell e.m.f.. The OP asks about B) measurement. We can distinguish between measurement of B1) Voltage and B2) Current though there are many other Electrical measurements. Voltage corresponds to fluid pressure in the hydraulic analogy and can usually be measured without disturbing the system. For this one uses a Voltmeter that draws only a negligible current; if even the few milli- or micro- amps that a moving coil meter draws would disturb then there are amplified VTVMs and FET-VMs with extreme high input resistance. (The corresponding pressure sensor in the hydraulic analogy has zero leakage.) However to measure an electric current (which is fluid flow in the hydraulic analogy) in the system it is usually necessary to disturb it by diverting some current to a measuring instrument. If the system current is large it is not necessary to divert more than a small fraction of it if a shunt resistor can be introduced in the current path. See Shunt_(electrical). A shunt allows almost any magnitude of current to be measured by means of a voltmeter that connects with lightweight wires to the shunt's two electrodes. Wnt mentions that a current flow can also be measured by the magnetic field it produces, which is the principle employed by the clamp-type current probe. Blooteuth (talk) 00:26, 16 July 2017 (UTC)

What is the difference between a magnet and the thingy that deionizes water?
Please don't direct me to electrodeionization, and the picture on that page, though relevant to this inquiry, seems to be in a foreign language. Anode is anode. Kathode is likely cathode. And the lines and arrows are the movements of water ions. But how is this different from a magnet? If I put a magnet with an anode and cathode in water, then will it deionize the water? I know extremely pure water is not drinkable, but if I put fruit purée or just sodium chloride, then will the water become drinkable? 50.4.236.254 (talk) 16:53, 15 July 2017 (UTC)
 * It is a myth that extremely pure water is not drinkable. (Just make sure your diet has other sources of the minerals you were previously getting from tap water, like magnesium and calcium.)
 * 
 * ApLundell (talk) 19:44, 15 July 2017 (UTC)
 * It's still not a good idea to drink it, if the deionizing water machine is located at work. That machine is likely for highly sensitive medical and scientific instruments. 50.4.236.254 (talk) 00:49, 19 July 2017 (UTC)
 * I agree with, although I'll also add that the taste of such water may not be optimal. — Paleo  Neonate  - 19:49, 15 July 2017 (UTC)
 * But the question is simple to answer: A magnet creates a magnetic field, while cathode and anode create an electric field. Icek~enwiki (talk) 19:55, 15 July 2017 (UTC)
 * Yes it seems this problem at least partially arises because you, the IP are once again failing to understand the basics before trying to understand something more complicated. "But how is this different from a magnet? If I put a magnet with an anode and cathode in water, then will it deionize the water?" You should read the article magnet. No where does it say anything about an anode or cathode. If you read those later two articles, they do mention magnetic fields but only in relation to the Etymology. You can explore further the articles of Magnetism and magnetic field to find neither of them mention anodes or cathodes. Of course it's possible a magnet could have had a anode and cathode with the terms having different meanings when it comes to magnetic fields which could cause confusion but this isn't the case, a magnet has a north and south pole. So again, the problem is not that the electrodeionization is a bad article (it may or may not be but that's beside the point) but you're reading stuff that isn't suitable for your level of understanding. Whether you want to read our articles or something else, you should find for yourself suitable sources on magnets if you think a magnet has an anode and cathode. (Perhaps you could say an electromagnet has an anode and cathode, but that's unrelated to the magnetism part.) Nil Einne (talk) 07:04, 16 July 2017 (UTC)


 * Well since you don't like the electrodeionization article can I direct you to the Capacitive deionization article instead, it isn't too different a process. Or Purified water which is what you get if you put 'deionization' into the search box and which has a section on 'Health effects of drinking purified water'. I fail to see where your idea of a magnet comes from, just because a diagram has an arrow in it does not mean there is a magnet involved. Dmcq (talk) 19:56, 15 July 2017 (UTC)


 * The diagram is in a foreign language (German), but the gist is clear to me. You have a - voltage at one end (cathode) and a + voltage at the other (anode).  Anions go ("ion" means "go" or "move") to the anode and cations go to the cathode.  (for confusion, cathode rays come from the cathode and have charge to match the cathode, which is the opposite charge from cations, i.e. cathode rays are negatively charged electrons so the - charge pushes them away, while cations are things like Mg++ with positive charge that pulls them in)  When you put an anode at one end of a big stack of membranes, all the - charges (anions) try to go to it.  But you split up the area with anion-impermeable membranes, so the anions stop.  Then, in between the anion-impermeable membranes, you put cation-impermeable membranes halfway.  So the cations stop when they hit them.  And when you look at the diagram, you see the geometry is that you have alternating areas where anions and cations get stopped, and form saltier solution, and then areas where they are coming from, which are desalinated to a greater degree.  You then pour off less-salty water from one half of the sections of the stack and more-salty water from the other half that are shuffled between them.  Really quite clever, nothing I ever imagined before just now.  But -- I have no idea what AAT, KAT, MB, KR in the diagram stand for.  There's a fair chance native speakers of German wouldn't have a clue.  There could be wide range of membrane materials and it seems like this might be one specific type... but who knows? Wnt (talk) 20:34, 15 July 2017 (UTC)


 * Despite having and OK-ish reading knowledge of German I couldn't really understand much of the schematic. So I deleted it. After all this is en:wp. Shock Brigade Harvester Boris (talk) 01:57, 16 July 2017 (UTC)


 * The abbrevs are explained in the German language article. Apparently, AAT=Anionenaustauschmembran (anion exchange membrane), KAT=Kationenaustauschmembran, MB=Mischbettionenaustauscher (mixed bed ion exchanger), KR=Konzentratraum (concentrate container(?)) Asmrulz (talk) 02:25, 16 July 2017 (UTC)

Which US coal basin deliver which coal?
Is there any Met coal coming from Illinois (Illinois Basin)? Or is it only Thermal coal?

Is there any Thermal Coal coming from Pennsylvania, or only Met Coal?--Zen priest (talk) 20:32, 15 July 2017 (UTC) File:Appalachian map.svg
 * Our articles are in a sorry state, and I'm certainly not an expert. In general, anthracite coal in the Appalachian Mountains has been subjected to metamorphism that has driven off impurities and made it purer and harder, and bituminous coal is softer, more similar to lignite and lower grades of coal (see coal for the full series).  However, coking coal, described as a form of metallurgical coal, can also be bituminous.  The level of sulfur is apparently very relevant, which may not perfectly relate to hardness grades ... should look into this further.


 * I suspect this question is prompted by a recent news item:  My impression is that anthracite mining traditionally was a more skilled art, in smaller angled veins or deep beneath the earth rather than in flat beds, and so the opening of a new mine with only 70-100 employees seems understandable.  Somerset County, Pennsylvania is right near the edge of the Valley and ridge province .. I imagine the geology would be fun to dig into.  But I would suspect that mines a little further west or north are going to be more like bituminous strip mines with lower-grade coal.  For example, this article suggests a mine that Scott Pruitt visited just a few counties to the west in Sycamore, Pennsylvania is being run by a company looking to get out of the business and faces decreasing demand.


 * Our article on anthracite lists some out of Pennsylvania reserves like Crested Butte, Colorado. I tried putting that through Google for metallurgical coal and it spat back this about a Las Animas, Colorado mine, the only metallurgical coal mine in the state.  So yes, there are such mines outside of Pennsylvania.  I didn't look up the orogeny but obviously there are some features in Colorado that could have caused some metamerism. Wnt (talk) 01:40, 16 July 2017 (UTC)


 * As for the Illinois Basin, well... I didn't quickly find any mention of metallurgical coal. The region is known for cheap, high-sulfur bituminous coal for burning .  My gut feeling is that even if there were the roots of a lonely mountain in the middle of the Illinois Basin surrounded by anthracite, it would by definition not be part of a geological basin.  But I don't know that! Wnt (talk) 01:47, 16 July 2017 (UTC)
 * According article Coke (fuel) Pennsylvania was a center of Coke and, always connected, steel production. Because of that connection and because of the troubled world steel production even established coke and steel production areas are struggling to stay in business.
 * Unfortunately for the United States steel production, and thus US coke production and thus US coal mining industry, is directly dependent on a wide array of local production industries that need lots of steel. That is where President Trump's plan to revoke US "clean coal" production seems to fall short. It was not the Paris climate accord that put US coal miners out of business, like Mr. Trump is trying to teach us recent history. The Financial crisis of 2007–2008 and the connected downfall of industrial production where the main reason most US miners lost their old job. --Kharon (talk) 08:43, 16 July 2017 (UTC)
 * Although the 2008 financial crisis was a factor, others were also significant: around that date a number of US mines were coincidentally beginning to exhaust their economically extractable reserves, and market share was increasingly being lost to expanding coal production in developing countries (see History of coal mining and Mine closure). As you allude, both US and UK steel production (major users of coal) faced increasing competition from cheaper suppliers in India and China from the 1970s onward (see the historical table in List of countries by steel production), but it's always politically easier to over-simplistically put the blame for industry declines on the alleged policies of one's recent/current political rivals, rather than on complicated long-term global economic factors. {The poster formerly known as 87.81.230.195} 94.12.69.7 (talk) 20:36, 16 July 2017 (UTC)

I think the question-asker sought for an explicit answer, not just educated guesses.--2003:D2:1BC5:BB68:8AD7:F6FF:FE7C:3409 (talk) 11:42, 17 July 2017 (UTC)