Welcome to the science section
of the Wikipedia reference desk.

Select a section:

WP:RD/S

Want a faster answer?

Main page: Help searching Wikipedia

How can I get my question answered?

Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
Post your question to only one section, providing a short header that gives the topic of your question.
Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
Don't post personal contact information – it will be removed. Any answers will be provided here.
Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
Note:
- We don't answer (and may remove) questions that require medical diagnosis or legal advice.
- We don't answer requests for opinions, predictions or debate.
- We don't do your homework for you, though we'll help you past the stuck point.
- We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

November 17

Greatest science achievements from Australia?

Textbooks in the U.S. on science all list historical achievements from the U.S. and Europe. Probably none from Australia? Wikipedia's article even on TV remote control and garage remote control all says invited in U.S. I would like to see a textbook used in Australian colleges on biology, chemistry, and physics - even horticulture, to see if they actually list inventions/discoveries from Australia? I already had an earlier discussion on this page that the 1st genetically-modified blue rose was done in Australia, with the help of a Japanese company. Wonder what are some other famous 1sts in Australia. I would imagine a horticulture/botany textbook from Australia will be vastly different than in the U.S. or U.K. Anyone have who were the 1st from Australia to win the Nobel prize in sciences? 67.165.185.178 (talk) 02:34, 17 November 2022 (UTC).[reply]

Start with Timeline of Australian inventions. List of Australian Nobel laureates may also be of interest. For a deeper dive, try Category:Australian science and technology awards-gadfium 03:40, 17 November 2022 (UTC)[reply]

One invention highly relevant to most communication here is WiFi HiLo48 (talk) 06:17, 17 November 2022 (UTC)[reply]

Adding bubbles to beer. --Jayron 32 12:33, 17 November 2022 (UTC)[reply]

What is the basis for which metal detectors detect liquids?

Which would mean, metals and liquids, have some common-ality. Does that mean metal detectors can detect water, but not ice? 67.165.185.178 (talk) 04:33, 17 November 2022 (UTC).[reply]

Detection by metal detectors is based on electrical conductivity, which is about seven orders of magnitude higher for metals than for water, fluid or frozen. In other words, metal detectors are just as useless for detecting liquids (other than mercury) as dowsing rods. --Lambiam 08:52, 17 November 2022 (UTC)[reply]

Yea, metal detectors in airports and court buildings do a good job detecting liquids, so. 67.165.185.178 (talk) 04:04, 20 November 2022 (UTC).[reply]

And dowsing can work. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:34, 20 November 2022 (UTC)[reply]

The liquid detectors used at airport security checkpoints are based on Raman spectroscopy or Computed Tomography (or a combination of both), typically using high-energy X-rays. These methods are completely different from the technology used in metal detectors. --Lambiam 19:39, 20 November 2022 (UTC)[reply]

Raman spectroscopy that will be the least bit useful at airport security checkpoints won't be using x-rays as their excitation. Typically, they will use something in the UV-Vis-NIR range. While X-ray Raman scattering is a thing, it's generally providing atomic level details on the core electrons, which isn't terribly useful from a security perspective. On the other hand, more traditional Raman spectroscopy in the UV-Vis-NIR range provide molecular information, and are particularly adept at detecting things like explosives (especially peroxide based explosives, which are otherwise difficult to detect as they lack nitrogen). You are correct that CT mainly uses x-rays. --OuroborosCobra (talk) 20:55, 20 November 2022 (UTC)[reply]

Oh wait, the metal detectors are for where the human walks underneath a metal detector (like for courts). The thing that detects liquids is the topography where the bag goes through in a tunnel? But the tunnel detects metals too, so the tunnel is running 2 things at the same time? But those wands that the security guards wave around you also detect liquids. 67.165.185.178 (talk) 01:06, 21 November 2022 (UTC).[reply]

What makes you think the wands the security guards have detect liquids? --OuroborosCobra (talk) 18:48, 22 November 2022 (UTC)[reply]

Experience. But this was from security from working at UPS / FedEx rather than going to court. In fact, the courts for state court are weaker than federal court it seems, for the walk-through, in which federal court metal detectors can detect a watch, the state courts do not. 67.165.185.178 (talk) 22:28, 22 November 2022 (UTC).[reply]

As far as I can find, your experience is incorrect. Wands are metal detectors. You would need something like backscatter X-rays or millimeter wave scanners for something like detecting liquids. Both of these are done with full body scanners, and not "wands". --OuroborosCobra (talk) 23:27, 22 November 2022 (UTC)[reply]

My mom's menstrual cycles

We don't answer requests for medical advice --Jayron 32 12:13, 17 November 2022 (UTC)[reply]

The following discussion is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

My mom has painful menstrual cycles every other one (her average menstrual cycles are about 30.5 days long. One menstrual cycle, she could barely feel it, but the other one seems to be the "hurtful" one. She takes a Midol whenever those cycles come. Why is that, I wonder? 67.215.28.226 (talk) 04:52, 17 November 2022 (UTC)[reply]

Questions asking for medical advice, which this is, are not allowed here. Sorry. --174.89.144.126 (talk) 05:33, 17 November 2022 (UTC)[reply]

Oh, okay. 67.215.28.226 (talk) 05:45, 17 November 2022 (UTC)[reply]

Without being diagnostic: consider the fact that women usually have two ovaries, and these usually ovulate alternately. What you describe is not uncommon; it's even a currently ongoing plot point in the webcomic Dumbing of Age. {The poster formerly known as 87.81.230.195} 90.217.47.60 (talk) 11:22, 17 November 2022 (UTC)[reply]

What has her doctor said about this? ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:11, 17 November 2022 (UTC)[reply]

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

Uatchitodon's tragic status

Does anyone else think of it as being really tragic and depressing that the only known venomous reptile of the Triassic period is only known from teeth? CuddleKing1993 (talk) 19:54, 17 November 2022 (UTC)[reply]

"We don't answer requests for opinions". --174.89.144.126 (talk) 21:49, 17 November 2022 (UTC)[reply]

I'm confident that no one else thinks that. There were doubtless other venomous Triassic reptiles but if we don't have their teeth there's no way we could know they were venomous. We can't even be sure that Uatchitodon was venomous. Shantavira|^{feed me} 09:36, 18 November 2022 (UTC)[reply]

South American Ceratopsids, WHEN?!

Considering that We already have Saurolophine Hadrosaurs and Panoplosaurine Nodosaurs in South America, there just had to have been Ceratopsids in South America as well that coexisted with Abelisaurids, but we have not yet discovered any ceratopsid fossils for some unexplainable reason, why? CuddleKing1993 (talk) 20:00, 17 November 2022 (UTC)[reply]

Fossils are discovered by chance. Probably, nobody has been lucky so far. Ruslik_Zero 20:36, 17 November 2022 (UTC)[reply]

Even among megafauna for whom it is expected to be reasonable to find preserved fossils, we have only ever found a tiny fraction of likely species. Fossilisation is so unlikely that scientists estimate that less one-tenth of 1% of all the animal species that have ever lived have become fossils. Far fewer of them have been found. Which is to say that even forming a fossil is such a colossally rare event that most species are not even expected to have any fossil remains to even find, and given that we've only ever discovered a tiny portion OF THAT tiny portion, it is plainly unsurprising that any one particular species may have existed, and we have not yet found it. --Jayron 32 13:14, 18 November 2022 (UTC)[reply]

November 18

GSF prefix to a vessel name

What does GSF stand for when preceding a ship's name?

I found the acronym in the Glomar Explorer article, but it's not explained there. I failed to identify the appropriate meaning in DAB GSF, either. I found it also in GSF Development Driller II, similarly without an explanation. I asked TheFreeDictionary (https://acronyms.thefreedictionary.com/GSF), but that seems futile as well. --CiaPan (talk) 12:46, 18 November 2022 (UTC)[reply]

I'm fairly certain it refers to GlobalSantaFe Corporation, an oceanic oil exploration and drilling company. --Jayron 32 13:10, 18 November 2022 (UTC)[reply]

phosphorus esters

I am not sure what phosphorus esters (as used by US EPA) is supposed to be exactly. Phosphate esters? Phosphite esters? Something else? --Leyo 22:34, 18 November 2022 (UTC)[reply]

I would guess (and it is a guess!) they mean organophosphates#Pesticides since that's the most common class that the EPA regulates. There are lots of such calculation packages but all the compounds that reach the market have to use measured data for their hydrolysis rates. See parathion at the PPDB for an example. Mike Turnbull (talk) 23:07, 18 November 2022 (UTC)[reply]

It seems to me that phosphorus is a misspelling of the adjective phosphorous. Here EPA's HYDROWIN is mentioned as estimating "hydrolysis based on esters, ... and phosphorous esters only". --Lambiam 08:04, 19 November 2022 (UTC)[reply]

Thank you. I've now checked the Phosphate Help of EPI Suite, in which the following is stated (incl. the spelling error in the 3rd word):

The HYDROWIN phoshporus compound update was limited to organic phosphorus compounds with the following structures:
       R1          R1
       |           |
     O=P-R2      S=P-R2
       |           |
       R3          R3
where R1, R2 and R3 are substituents with the first atom being carbon, oxygen, sulfur, nitrogen, or halogen.

Hence, phosphorus esters is used for the group of phosphates, phosphonates, thiophosphates and other organophosphorus compounds that are esters. --Leyo 11:15, 21 November 2022 (UTC)[reply]

November 19

Green leaves in winter

I've noticed some deciduous trees retain several green leaves in winter (by November at least, like so). Why is that? 212.180.235.46 (talk) 15:36, 19 November 2022 (UTC)[reply]

It doesn't look to me like they've retained much of anything. Like chemistry, biological process (which are built on chemistry) rarely go to 100% completion, or at least not in a timely manner. 99% completion is pretty great. --OuroborosCobra (talk) 16:29, 19 November 2022 (UTC)[reply]

Since when is November part of winter? Even ignoring the Northern Hemisphere-centrism, neither the meteorological nor the astronomical definition of winter stretches that far. --User:Khajidha (talk) (contributions) 17:13, 19 November 2022 (UTC)[reply]

At 1st I thought this was a color question, so genetics, but the image and discussion makes it seem this is more of a wind question? Because the wind didn't blow it hard enough yet? 67.165.185.178 (talk) 17:17, 19 November 2022 (UTC).[reply]

See marcescence which is:-

...the withering and persistence of plant organs that normally are shed, and is a term most commonly applied to plant leaves. The underlying physiological mechanism is that trees transfer water and sap from the roots to the leaves through their vascular cells, but in some trees as autumn begins, the veins carrying the sap slowly close until a layer of cells called the abscission layer completely closes off the vein allowing the tree to rid itself of the leaf. Leaf marcescence is most often seen on juvenile plants and may disappear as the tree matures. It also may not affect the entire tree; sometimes leaves persist only on scattered branches.

Alansplodge (talk) 13:14, 21 November 2022 (UTC)[reply]

Weird, I can't tell the difference between marcescence and abscission for tree leaves that drop. 67.165.185.178 (talk) 02:58, 23 November 2022 (UTC).[reply]

The article Evergreen discusses broad-leaved trees that don't lose their leaves (like live oak, holly, southern Magnolia, etc.) There are sections which discuss why some of these trees don't lose their leaves. --Jayron 32 14:14, 21 November 2022 (UTC)[reply]

Machine printing on porcelain

In the history of art, it is said that the impact of the industrial revolution on porcelain manufacturing displaced artists from that profession because it allowed machines to print the designs directly on china, particularly in the early to mid-19th century. However, I cannot find anything about this technology or its inventors on Wikipedia. Can someone point me in the right direction? Thanks. Viriditas (talk) 20:07, 19 November 2022 (UTC)[reply]

The most relevant coverage on Wikipedia that I can find is Decalcomania. Think something similar to decals and transfer paper, or temporary tattoos popular with little children. The porcelain had an initial glazing. The pattern was printed on transfer paper, and then transferred to the surface of the porcelain item. Then, a transparent glaze was applied and the item was fired again. The technique goes back to about 1750. Take a look at Ceramics and Print, a book that has a chapter about the early history, starting on page 15. Cullen328 (talk) 20:27, 19 November 2022 (UTC)[reply]

Transfer printing also discusses the technique. Cullen328 (talk) 20:30, 19 November 2022 (UTC)[reply]

As I understand it, equipment that allowed machine printing directly on porcelain items without an intermediate transfer process was developed around the turn of the 20th century. Cullen328 (talk) 20:37, 19 November 2022 (UTC)[reply]

Thanks. The statement is made frequently in the art literature regarding French porcelain manufacturing in the 1850s. Just guessing, but there seems to be some secrecy surrounding the process, which is why there is little to nothing said about it. Viriditas (talk) 20:47, 19 November 2022 (UTC)[reply]

There is a technique using a soft rubber stamp, a bit like a flat soccer ball. The rubber is pressed against the inked flat pattern and then pressed against a plate, bowl or saucer. I've seen it done, but can't recall the correct name. Found it! "bat-ware", see Transfer_printing#Process. Martin of Sheffield (talk) 20:51, 19 November 2022 (UTC)[reply]

This is from German art historian Peter H. Feist (1987). "Renoir only spent four years as a porcelain painter. The industrial revolution made an immediate and irreversible impact on his life: a machine for printing pictures on china had been invented, which made him and many other porcelain painters redundant." The biographical article on Renoir says "the porcelain factory adopted mechanical reproduction processes in 1858" forcing him out of his chosen profession.

See also Théodore Duret (1910): "The decoration of porcelain [in the 1850s] had hitherto been done by hand, but now a machine was invented which rendered hand labour unnecessary. Porcelain painters were suddenly deprived of their means of livelihood." Viriditas (talk) 21:14, 19 November 2022 (UTC)[reply]

The "flat soccer ball" machine sounds more like pad printing. DMacks (talk) 21:28, 19 November 2022 (UTC)[reply]

Yamanaka-Method

Is there a detailed technical description of the method to abrogate adult stem cell differentiation? 2A02:908:424:9D60:1728:3390:1D6B:BA69 (talk) 21:04, 19 November 2022 (UTC)[reply]

Reference [17] in our article Induced pluripotent stem cell is the publication in which Yamanaka and his group describe their method for reprogramming human cells to become pluripotent. I have not read it and don't know if it is sufficiently detailed to allow replication. --Lambiam 05:42, 20 November 2022 (UTC)[reply]

November 20

Are there any naturally occurring conjoined flowers?

As in multiple flowers coming from the same body, like branches coming from the same tree? 67.165.185.178 (talk) 17:47, 20 November 2022 (UTC).[reply]

Do you mean Fasciation? Shantavira|^{feed me} 18:04, 20 November 2022 (UTC)[reply]

No. I wonder if I'm thinking about bushes, that can have multiple flowers sprouting out? 67.165.185.178 (talk) 01:07, 21 November 2022 (UTC).[reply]

Depends on how close together you want them to be. Nearly every flowering plant produces many flowers at once. A bunch of flowers clustered together on one branch is an inflorescence. ℰmi1y_⧼T·C⧽ 08:56, 21 November 2022 (UTC)[reply]

What we think of as a single dandelion flower actually consists of many tiny flowers, packed tightly together on a joint base. Each individual tiny flower produces its own tiny seed with a stalk ending in a downy "parasol". --Lambiam 10:44, 21 November 2022 (UTC)[reply]

November 21

Digital vs analog volume controls for fidelity

I've read from various non-authoritative sources online that given the choice between a digital volume control and a potentiometer to adjust the volume of sound, I should use the latter (as long as the former isn't set to cause clipping). This makes sense for minimizing quantization noise, since it keeps all the possible digital levels available; but how much difference does it make if other sources of noise are accounted for? For example, will a potentiometer always reduce the DAC's noise floor as much as it reduces the signal? Neon Merlin 02:01, 21 November 2022 (UTC)[reply]

Digital volume control does not diminish the number of digital levels. For a simple example, assume the levels of the source are 0, 1, 2, 3 and 4. Then perhaps on the max control setting you get 0 V, 0.50 V, 1.00 V, 1.50 V and 2.00 V. One notch lower may give you 0 V, 0.45 V, 0.90 V, 1.35 V and 1.80 V. So there are still five levels. There is no control setting that will turn input level 4 into output 1.90 V, but the jump from 2.00 V to 1.80 V corresponds to 0.9 dBV, which is barely noticeable. --Lambiam 10:20, 21 November 2022 (UTC)[reply]

A potentiometer alone doesn't affect the Signal-to-noise ratio of an analog signal and has no useful effect on a digital signal. A potentiometer at the input to a DAC is useful to avoid overloading the DAC but any further reduction of the input signal leaves some conversion levels unused, resulting in poorer quantisation noise than the DAC with its given number of resolution bits is capable. A Digital potentiometer is a digitally controlled circuit that may be used to scale an analog signal, or it may be a multiplying function incorporated in a DAC. The Signal-to-(quantising plus random)noise ratio established at the analog to digital conversion cannot be improved but it may be worsened if the final digital output lacks extra resolution bits to encompass data MSB when gain >1 (amplification) is applied and to retain data LSB when gain <1 (attenuation) is applied. Philvoids (talk) 20:15, 21 November 2022 (UTC)[reply]

Is the question about controlling the volume at the input to a digital recorder, or at the output? My response above assumed the latter. --Lambiam 19:16, 22 November 2022 (UTC)[reply]

There's a number of factors which can make potentiometers start getting a bit crackly especially if they've got a high resistance or are old. And if they are a wiper running over a coil you're digitising anyway :-) NadVolum (talk) 23:17, 21 November 2022 (UTC)[reply]

Potentiometers with logarithmic resistance tracks suited to audio volume control are susceptible to scratchy wear. A design advice is to add a capacitor to block direct current through the slider and its tiny contact point on the track. Philvoids (talk) 12:21, 22 November 2022 (UTC)[reply]

measuring oxygen level in air

Short video longer similar one The short (30 sec) video shows the experiment, longer one has explanation. The idea is that burning a candle inside a closed jar creates vacuum in the jar, as O2 is consumed. The vacuum is measured by water lifted into the jar. About 20% of the jar's volume is filled with water, so that means 20% of the air is gone. The part that is gone is the oxygen, and the part remaining is nitrogen and other insert gases.

Question: why isn't some of the gas CO2? Is there a way to calculate the amount? If I did that experiment in a pure O2 atmosphere, would the whole jar fill with water? Thanks. 2601:648:8200:990:0:0:0:4775 (talk) 05:29, 21 November 2022 (UTC)[reply]

There would be some carbon dioxide. The burning wax make water vapour and carbon dioxide, and later may yield carbon monoxide. The steam will mostly condense into the water anyway. Carbon dioxide will also dissolve a bit in the water. You might get a truer result if you burn something that has a solid combustion product, eg steel wool. Graeme Bartlett (talk) 06:22, 21 November 2022 (UTC)[reply]

Thanks. I did find some pages about using steel wool, but it apparently takes a long time, like days. You wait for it to slowly oxidize, at least on the pages I found. I don't need a very precise measurement so if the CO2 and CO don't affect it too much, I will try to find a way to do the candle method. The complication is that I'm trying to test the output of an O2 generator rather than atmospheric air, so I have to get the generator output into the jar and then light the candle, but I think I can find some hacky way to do that. 2601:648:8200:990:0:0:0:4775 (talk) 06:30, 21 November 2022 (UTC)[reply]

A small spark will ignite steel wool, so if you include a spark plug (as part of a powered circuit you can close from the outside), you can set the reaction off while the jar is closed off from surrounding air. --Lambiam 10:29, 21 November 2022 (UTC)[reply]

Hmm you mean a car spark plug with an ignition coil? Seems way overboard. I might order some nichrome heating wire which could maybe also work. I had figured to use it to ignite a match tip, and use the match to light a candle. The idea is to just do a crude estimate in my kitchen, not anything lab grade. The electric ignition is because I'll have to immerse the jar in water, then collect oxygen in it from a plastic tube, then light the candle. Another way might be to use a flex-type barbecue lighter but idk how well that would handle being partly immersed in water. I'll keep thinking about this. Thanks. 2601:648:8200:990:0:0:0:4775 (talk) 10:48, 21 November 2022 (UTC)[reply]

I've no idea about your background, so this is simply a friendly warning. Please be aware that normal, slow, combustion can accelerate to very fast, hot and intense burning in the presence of pure oxygen. You need to ensure that your containers can tolerate the sudden increase in temperature and, depending upon your setup, pressure. As an absolute minimum wear eye protection in case of glass shattering. There's a video here which is designed for medics showing how oxygen makes fires far hotter and fiercer. Martin of Sheffield (talk) 12:05, 21 November 2022 (UTC)[reply]

If you use steel wool as the fuel, you do not need a candle, just enough steel wool. Apparently you can use steel wool directly as the heating element as well.^[1] --Lambiam 18:40, 21 November 2022 (UTC)[reply]

Lambiam, I think I would have trouble igniting the steel wool with a spark since I don't see how to avoid immersing it in water while collecting the oxygen. Jayron32's suggestion wet steel wool sitting for a week might be doable, though I'd have to do a jar with ordinary air to compare. Actually just waiting 1 day or so might be enough to see a difference in the oxidation speeds. Martin of Sheffield, good point about safety glasses. 2601:648:8200:990:0:0:0:4775 (talk) 05:54, 22 November 2022 (UTC)[reply]

It is possible to ignite steel wool by passing electricity through it. You don't need a spark plug and thousands of volts. Just have a pair of wires and have a few amps passing through the wool will heat it up till it burns. Graeme Bartlett (talk) 10:20, 22 November 2022 (UTC)[reply]

If you follow the link in my reply above, you'll see a method not involving a spark. It may not work well, though, with wet steel wool. --Lambiam 10:24, 22 November 2022 (UTC)[reply]

The "about 20% rise of the water due to about 21% original oxygen content of air" is a great example of a logical fallacy (and one that can easily be explained alternately and even disproved), though I can't remember the correct term for this specific mistake. The easy forgotten detail is that the air around a burning candle is hot whereas the jar is cool. Cooling the air near the candle causes a decrease in pressure and therefore water is pulled up into the jar. Here's a good detailed explanation of that, a way to prove it, and yet another interesting idea related to it: [2]. DMacks (talk) 18:15, 21 November 2022 (UTC)[reply]

The air in the container is initially in thermal equilibrium with the outside air. The burning will heat the air, so the pressure rises and will push the water down until the pressure is equalized. On the other hand, the volume of the hot air decreases because of oxidation removing O₂, so the water will rise. It is not immediately clear which of the two counteracting effects will be the stronger, but that is not relevant. In the end, the air will cool down to thermal equilibrium again, and only the effect of the volume reduction remains. --Lambiam 18:52, 21 November 2022 (UTC)[reply]

I have to agree with DMacks. The crude way that the candle experiment is usually performed would mean that temperature differences (and hence pressure differences) likely play a large role in the result. Even just lowering a jar over a lit candle is going to trap hot air, which will lead to volume changes when it cools. In addition, burning wax will (mostly) create carbon dioxide and water, but the portion that is carbon dioxide will still continue to occupy space in the jar, so even complete consumption of the oxygen would not be expected to reduce the volume by 20%. Dragons flight (talk) 09:22, 22 November 2022 (UTC)[reply]

IIRC When I worked in a school lab (decades ago) we added some (can't recall how much) bench sodium hydroxide solution to the water to ensure CO2 absorption.Martin of Sheffield (talk) 09:38, 22 November 2022 (UTC)[reply]

My interpretation of the envisaged experiment was that by some still-to-be-determined method (like nichrome wire igniting a match lighting the candle) the candle was going to be lit after the container is sealed off. --Lambiam 10:33, 22 November 2022 (UTC)[reply]

If I do the thing with the nichrome wire, it will also be easy to check whether there is vacuum created by just heating the air by electrical resistance, with no candle. Yes the idea of igniting the match with a nichrome wire is to be able to light the candle after the jar is sealed. It seems like a pain and I will keep thinking about alternatives. 2601:648:8200:990:0:0:0:497F (talk) 06:44, 23 November 2022 (UTC)[reply]

I've done the activity many times, but with wet steel wool over the course of about a week or so. As the steel wool rusts, it will react away the oxygen from the air. Burning is faster, but not strictly necessary. I just set the apparatus up on the desk at the front of my classroom, and let it react slowly. The water will rise inside the test tube about 1/5 of the way and then stop rising. It's usually good enough for a quick demonstration for school children. See here for an example of how to do it. --Jayron 32 19:02, 21 November 2022 (UTC)[reply]

November 22

Two questions regarding electrical & thermal conductivities in metals and incandescence

a. Wiedemann-Franz law is an empirical law indicating the linear relation between electrical & thermal conductivities. What's the underlying microscopic-quantun explanation ? After all, thermal electronic motions are random in all directions, but electrical conductance is directional (opposing the electrical field).

b. What's the physical mechanism explaining the continuous spectrum emitted when an electric current flows through it (e.g., in an incandescent lamp or a oven) ? again, the question focuses on the fundamental description, on the basis of the electronic band structure in metals. Thanks, בנצי (talk) 20:58, 22 November 2022 (UTC)[reply]

a. The W–F law applies to metals, in which some electrons are not bound to atoms but can move around, the higher the electrical conductivity, the more freely. These electrons carry not only a charge, giving rise to an electrical current, but also thermal energy, giving rise to a flow of heat. Consider that the motion of the particles of a gas is also random in all directions. What gets transferred as heat are not the particles themselves, in this case electrons, but their kinetic energy.

b. In a sufficiently hot material, hot to the point of incandescence, the atoms and therefore the electrons and protons are violently jostled around, with velocities that can be modelled as a three-dimensional continuous Gaussian distribution. Since they are charged, their motion produces electromagnetic radiation, which in this situation is called thermal radiation.

--Lambiam 00:24, 23 November 2022 (UTC)[reply]

a. Your comments here repeat known facts, already included & implied in the question. Hence, I'll pinpoint & emphasize it. 1st, let me make a comment on your last phrases: what is transferred isn't just Ek, since the process of collisions between electrons & (metallic) ions on the line of the electric field is a very slow one (drift velocity). So the picture of conductance is more complicated - the energy is transferred like an EM wave. So it's not the mere charge motion. Moreover, this phenomenon depends on the existance of phonons etc. These are the background of my question. To conclude the focus of the 1st question, why electric & thermal are linearly dependent ?

A relevant remark: pay attention to fact that thermal energy transfer is slow, while the electric one is (much) fast(er).

b. Essentially, your answer here is based on the classical model of accelerating or decelerating charges, while in the question the QM picure was addressed - typical metallic energy band structure of the electrons.

c. Following the above discussion, how these two models (classical & QM) correspond to each other ?

@בנצי: Your harsh dismissal of Lambiam’s answer was unwarranted. You did link to the Wiedemann-Franz law, but you called it an "empirical law" and asked for a "microscopic-quantun [sic] explanation". It seemed reasonable to infer that you had not read or understood that article fully, as the section Wiedemann–Franz law#Derivation (the first section past the lead, with a fairly explicit name) explains that the linear relationship follows easily if you assume both transport phenomena follow the Drude model. Lambiam’s level of explanation was perfectly reasonable in light of these assumptions.

I do not know if the problem is poor communication, or a "knowledge exceeds wisdom" issue. In either case the problem was squarely on your end; but even if it had not been, you should still remain civil. Tigraan^{Click here for my talk page ("private" contact)} 10:53, 23 November 2022 (UTC)[reply]

Sharpness & focusing aren't harshness, and your comments don't contribute to the discussion. The original question was very clear, and I don't see why you find saying "empirical" a problem. Well, it's not a fundamental law but an empirical one, and was quoted to indicate the linear relation between the two phenomena. I was sorry to find & read this response of yours, let alone postulating on a "perfectly reasonable" with no substantiation on physics grounds, and apologize for having a professional standpoint, and even critical. Raising a question should not lead to inferiority, let alone comments regarding the extent of civil. My intentions were completely honest & genuine, trying to get better insight/s into the mentioned topic. The answers led to none.

Maybe "poor communication" or maybe not. Many thoughts & efforts were made to phrase the questions clearly, but they seem being diminuated, which is insulting enough, let alone taking the position of a judge, in the personal comments like "wisdom", "squarely" blaming me, and the "civil". Thank you very much indeed.

Eventually, I'll find out about what were asked elsewhere, and maybe add it here for the benefit & completion of the discussion, for all. בנצי (talk) 11:56, 23 November 2022 (UTC)[reply]

I have no doubt that you have genuine intentions to learn, and I think you were not uncivil enough to warrant sanctions.

You seem to think that your post is entirely clear, and that Lambiam’s answer was useless. Fine, here’s a simple solution: let’s wait and see if someone else answers. If you don’t get any further replies, it must be because nobody on the RefDesk is qualified in those topics. In that case, make sure to post it on https://physics.stackexchange.com/ and give us a link so we can read the answers and be enlightened. Tigraan^{Click here for my talk page ("private" contact)} 13:00, 23 November 2022 (UTC)[reply]

I found neither harsh nor uncivil exressions in the OP's response to the first responder.

WF law has two aspects: the empirical one, and the theoretical one the OP asks their question about. Please note that this law really has the empirical aspect, in the sense that this law can be experimentally verified (at least in the specific cases checked out in the experiments), as opposed to some physical arguments which (hypothetically) can only be refuted yet not be verified (like many well known astrophysical theories, and even many mathematical hypotheses, e.g. "this random infinite sequence of digits contains no zeros", and the like, while WF law is different because it can also be experimentally verified). Anyway, the OP only claimed that this law, having its empirical aspect, must (probably) also have its quantum theoretical background, so what is it?

I won't be surprised if it turns out that the OP was one of the main contributors to our article about WF law. Anyway, I couldn't find out how your comment about "knowledge exceeds wisdom" could help.

As far as I could understand, the OP's first question is clear: An electric flow is measured as a vector, while heat is measured as a scalar, so how can this vector and this scalar be linearly related to each other, from a quantum theoretical viewpoint? How does Drude model explain this linear connection?

A last comment, but to the OP this time: Maybe you should have introduced yourself, before you asked your question on this reference desk, beacuse the previous editor could see no userpage of yours. סמי20 (talk) 18:39, 23 November 2022 (UTC)[reply]

I am not convinced by the remark that "thermal energy transfer is slow, while the electric one is (much) fast(er)" is an essential fact because a practical measurement of either must be affected by a finite thermal or electrical capacitance respectively. Philvoids (talk) 20:02, 23 November 2022 (UTC)[reply]

"Not convinced" in what ? what claim is not convincing ? Hold an iron bar in its end, while the other end is put in flame. You must be knowing you don't have to remove your hand too immediately. Hoever, making a call to you on the phone intercontinentally for example, or sending this reply via Wiki interface, require ~microsec. בנצי (talk) 11:23, 24 November 2022 (UTC)[reply]

The iron bar has an isobaric heat capacity of 25.09 J⋅mol−1⋅K−1. That has to be taken into account in your estimate of "time to say 'ouch' ". Philvoids (talk) 14:33, 24 November 2022 (UTC)[reply]

Yes, electric flow is measured as a vector, while heat is measured as a scalar. Conductivity, however, whether electrical or thermal, is neither. It measures the effect of applying a difference (voltage or temperature). One might just as well offer the objection that charge is measured as a scalar, while heat flow is measured as a vector. It is equally irrelevant. --Lambiam 20:04, 23 November 2022 (UTC)[reply]

Current is not vector, and it's a mistake said previously. — Preceding unsigned comment added by בנצי (talk • contribs) 11:31, 24 November 2022 (UTC)[reply]

The current density is definitely in essence a vector quantity.

In many useful applications, electricity can be assumed to flow along a single axis (because the length of a wire is much greater than its diameter). Then one can reason in of scalar properties (current, resistance), use Ohm’s law in scalar form, etc. Similarly, when looking at a one-dimensional heat transfer problem, one can use scalar values: for instance, if a thin insulating layer is placed on a large section of wall, the (vector) heat flux is mostly perpendicular to the surface, and one can reason as if temperature / flux varied only along that axis.

However, when looking at a problem where multi-dimensional effects are important, one needs to consider the vector formulation of current density, electric field etc.

There’s another subtlety of intensive and extensive properties - for instance current, an extensive property, is the product of the (intensive) current density times the cross-section of the wire; but it’s not really relevant, one can define a scalar current density just fine. Tigraan^{Click here for my talk page ("private" contact)} 14:07, 24 November 2022 (UTC)[reply]

@20סמי:,

Thank you for your nice & relevant contribution to this discussion, and I'd like to make a few comments:

a. W-F law applies not to "special cases", but proved for metals due to their common structure & their consequent properties. בנצי (talk) 12:13, 24 November 2022 (UTC)[reply]

Oh, I didn't write it applies to special cases. Of course, it's a physical rule, so it must be universal (regarding metals), so it's supposed to apply to all cases. Maybe I had to add more words to my previous response, for making it clearer. I've only indicated that WF law (like every physical law) is experimentally verified at least in the specific cases checked out in the experiments. Like every physical law. Actually, no physical law can be experimentally verified for all cases, because the set of all cases is infinite. For exmaple, if I measure the mass of one electron, the result is valid for this electron only. For this result to be valid for a second electorn, one has to repeat the experiment for the second electron, and so forth. This principle is true for all physical laws, including WF law, and I'm sure you agree. סמי20 (talk) 16:59, 24 November 2022 (UTC)[reply]

b. Current isn't vector. בנצי (talk) 12:13, 24 November 2022 (UTC)[reply]

Oh, I didn't write current is a vector. I've only indicated it's measured (e.g. by it's density) as a vector. Anyway, I had to be more precise, because you were asking about the electrical conductance, i.e. the ratio of current to voltage. סמי20 (talk) 16:59, 24 November 2022 (UTC)[reply]

c. Drude model isn't the most update one, and is capable of explaining only some of metal properties. בנצי (talk) 12:13, 24 November 2022 (UTC)[reply]

@Tigraan, are you hearing? סמי20 (talk) 16:59, 24 November 2022 (UTC)[reply]

d. Self-introducing. Well, good idea, but better to be raised in the 'talk' page. בנצי (talk) 12:13, 24 November 2022 (UTC)[reply]

I'm sure if Tigraan had seen your userpage, they wouldn't have thought what they still think about you. Actually, you are more than a username: You are an individual, a person, a human being, and as such you may own several usernames on Wikipedia, so I still claim I won't be surprised if it turns out you are one of the main contributors to our article about WF law (not necessarily under your current username). סמי20 (talk) 16:59, 24 November 2022 (UTC)[reply]

I won't be surprised if it turns out that the OP was one of the main contributors to our article about WF law You know you can check that, right? (The answer is no.)

A last comment, but to the OP [...] Nobody is under any obligation to create a userpage or introduce themselves to edit Wikipedia, and the RefDesk is no exception. I do not modify the answers I give based on the identity of the person who asks (except maybe if the question is clearly susceptible of two interpretations, and I can guess which interpretation to take based on that, but that’s rare). If anyone is provably giving poor-quality answers to people they do not know or like, I support the usual escalation mechanism towards sanctions (friendly warning on talk page, if it fails stern warning, if it fails admin actions).

The OP’s command of English is poor (presumably because it is not their native language); there is no shame in that, but it does impede communication. There might also be a cultural barrier thing, where a perfectly acceptable sentence in one language becomes too harsh when translated in another language. Speaking for myself, I find Your comments here repeat known facts... pay attention to fact [sic] that... to be much harsher than what one would reasonably expect to find in a Q-and-A session.

Finally, I will elaborate on my "knowledge exceeds wisdom" line. I suspect that OP believes they have understood many things which in fact they have not mastered, moved on to much more complex topics, and as a result of that asked a poorly-formulated question (the abovementioned English difficulties compounding it). For example, suppose that someone asks why humans still exist, when our article Cretaceous–Paleogene extinction event says that no tetrapods weighing more than 25 kilograms (55 pounds) survived. Answering that question requires to make assumptions about what misconceptions the asker might have (for instance, do they believe humans coexisted with dinosaurs?); it might require counter-questions to find out where the misunderstanding is.

If you look at the original question, it is hard to tell if the OP would be best served by a basic explanation of how electrons conduct electricity, a hand-waving explanation of Drude model basics, or a technical discussion of the limitations of Drude and alternative models; or an analysis of experiment vs. models for the WF law; or something entirely different. Their following comments do not help much, either. Tigraan^{Click here for my talk page ("private" contact)} 14:45, 24 November 2022 (UTC)[reply]

November 23

Truth of claims

All Indian school books continuously tell school kids that Jagadish Chandra Bose first proved that life exists in plants

https://twitter.com/ParveenKaswan/status/1595246772191784962

https://www.indiatoday.in/education-today/gk-current-affairs/story/jagadish-chandra-bose-plants-life-322594-2016-05-10

and he independently invented radio wave receiver.

https://www.indiatoday.in/education-today/gk-current-affairs/story/jagadish-chandra-bose-839079-2016-11-30

https://theprint.in/features/j-c-bose-father-of-radio-science-who-was-forgotten-by-west-due-to-his-aversion-to-patents/552556/

Does American, European science community accepts this? 2402:3A80:1A42:7664:DCB1:A557:55EC:9355 (talk) 03:33, 23 November 2022 (UTC)[reply]

It is rather unclear what the statement means. Therefore it is not possible to say whether any scientific community accepts this. You might as well say that early Indian astronomers proved that the Moon exists in the sky. The second link states: "Before the advent of the 20th century, science did not acknowledge the vitality of trees and plants." Bose is credited with showing this botanical vitality. But any farmer, since prehistoric times, was aware of the vitality of plants. If by "vitality" the concept of the theory of vitalism is meant, then you should be aware of the fact that in today's scientific consensus this is a bogus theory, and "proving" it does not earn one credit. Long before Bose, Erasmus Darwin, a grandfather of Charles Darwin, argued in his book Zoonomia that vegetable life and animal life sprang from a common source and were not fundamentally different. What is certain is that Jagadish Chandra Bose was the first to propose the theory that plants have an internal signalling system, as laid down in his book The Nervous Mechanism of Plants. While the significance of the theory is acknowledged, I think that the consensus is that his experiments did not establish his precise claims, in particular the existence of signalling pathways in plants conveying electrical signals carrying messages. Instead, plants use phytohormones, which are chemical compounds. --Lambiam 07:50, 23 November 2022 (UTC)[reply]

Regarding the radio wave claim... For some reason, many people want to claim the "inventor of the radio" for their country. (See Talk:Guglielmo Marconi and the archives thereof.) My reading of our (detailed) article invention of radio is that:

The early theoretical work on radio waves in general was mostly Hertz/Maxwell
Many prototypes of detection apparatus were created in the 1890s, by many researchers. Yes, that includes Bose, but also others with roughly equal contribution (Branly, Lodge, Popov).
The first working long-range communication devices were definitely Marconi’s.

Tigraan^{Click here for my talk page ("private" contact)} 12:36, 23 November 2022 (UTC)[reply]

And don't forget the contributions of Nikola Tesla. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:22, 23 November 2022 (UTC)[reply]

Year 2038 problem

Will my computer suffer the Year 2038 problem? 67.215.28.226 (talk) 20:43, 23 November 2022 (UTC)[reply]

Will you still have the same computer in 16 years time? Martin of Sheffield (talk) 20:50, 23 November 2022 (UTC)[reply]

Maybe... 67.215.28.226 (talk) 20:52, 23 November 2022 (UTC)[reply]

And assuming I do have the same computer in 16 years, my computer is a Windows 11 with a 64-bit operating system. 67.215.28.226 (talk) 21:15, 23 November 2022 (UTC)[reply]

The Year 2038 Problem can manifest itself at any time when dates after 2038-01-19 03:14:07 are considered; you don't actually have to wait until then. OR, but I am already aware of an instance where a company (or perhaps their legal department) requested a 20-year software license key - and it failed as expired. catslash (talk) 21:45, 23 November 2022 (UTC)[reply]

Okay. 67.215.28.226 (talk) 22:28, 23 November 2022 (UTC)[reply]

@Catslash: My friend experienced a somewhat similar problem in late 1990's: at some point the results of periodical work-related medical examinations of his employees started to be automatically invalidated by the HR system due to expiration, as a result of 'wrapping' a year last-two-digits representation from the range 2000 .. 2002 into 1900 .. 1902. :) --CiaPan (talk) 00:26, 24 November 2022 (UTC)[reply]

The Year 2038 problem affects systems which store time as seconds since 1970 in a signed 32-bit integer. This format originated in Unix systems, although it's possible that some parts of some older Windows systems also do this. But a 64-bit Windows 11 system almost certainly doesn't store time in a 32-bit variable anywhere in the operating system. The only problem would be if you are running a particular application which stores time this way. CodeTalker (talk) 23:49, 23 November 2022 (UTC)[reply]

Okay, good! Thank you. 67.215.28.226 (talk) 02:28, 24 November 2022 (UTC)[reply]

If you wish, it is possible to do the experiment now merely by setting your computer's clock to a few minutes before the timestamp you are worried about, switching off its automatic timing updates, if it has them, and seeing what happens. I know that this was how some IT folk tested whether their systems were going to hit the Year 2000 problem and they would need to do something about it. Mike Turnbull (talk) 18:13, 24 November 2022 (UTC)[reply]

This isn't for the computing desk huh? 67.165.185.178 (talk) 10:25, 24 November 2022 (UTC).[reply]

November 24

Pumping water

Suppose I wanted to pump water at a rate of 5m³/s to a height of 5m. How much energy would that require in kW? If I doubled the height to 10m, would it require double or quadruple the energy? Mjroots (talk) 07:56, 24 November 2022 (UTC)[reply]

From my very rusty physics:

5m³ weighs 5,000 kg, so exerts a force downwards of 5,000g N. To lift this water 5m would therefore take 25,000g J. To do it in one second (ie 5m³/s to a height of 5m) requires 25,000g W, that is 25g kW or roughly 250 kW. All assuming no losses anywhere in the system. To lift to twice the height would indeed require twice the input. Martin of Sheffield (talk) 08:44, 24 November 2022 (UTC)[reply]

That's good news, was fearing that double the increase of height would result in a quadrupling of the energy required. Mjroots (talk) 13:18, 24 November 2022 (UTC)[reply]

You will have to ensure that your pumps can deliver the higher pressure, 10m of water is near enough 1 bar. As the pressure increases the efficiency of the pump (particularly for non-displacement types) will reduce. With any luck a hydraulic engineer will happen along soon. Martin of Sheffield (talk) 14:15, 24 November 2022 (UTC)[reply]

@Mjroots For the details, see Potential_energy#Potential energy for near Earth gravity. U=mgh, not accounting for any losses owing to your pump not having 100% efficiency. Mike Turnbull (talk) 18:18, 24 November 2022 (UTC)[reply]

As MoS said, 250 kW and 500 kW. I'm not a pump engineer, but I am an engineer with a lot of pumps. So you need to look at the discharge curve for the pump. A 250 kW mixed flow pump will cost a many many thousands of dollars, it is a substantial piece of gear. https://www.torishima.co.jp/en2/pdf/products/smsv_smiv.pdf You'll also need 250 kW of electricity to run it. Greglocock (talk) 22:37, 24 November 2022 (UTC)[reply]

Mirrors.

What is the process of converting glass to mirrors, and mirrors back to glass? I'm assuming mirrors are made from glass as a precursor. 67.165.185.178 (talk) 21:20, 24 November 2022 (UTC).[reply]

The typical mirror I've seen is just a piece of glass with a thin coating of silver on the back. It's the silver that provides the reflection. You might find out more in the Mirror article. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:18, 24 November 2022 (UTC)[reply]

November 25

Closest point from North America to Africa?

What's the closest point from North America to Africa? 67.215.28.226 (talk) 03:10, 25 November 2022 (UTC)[reply]