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October 16

Are eggs created in the body of birds by stem cells?

What is the main type of cell in birds which makes the "genesis" of eggs?

Thanks, 49.230.20.227 (talk) 00:36, 16 October 2021 (UTC)[reply]

In birds, as in mammals, oogenesis proceeds from oocytes, specialized cells in the ovaries. The unfertilized egg (or fertilized but before embryogenesis has begun) itself is one cell. --Lambiam 08:53, 16 October 2021 (UTC)[reply]

SI unit in Electro chemistry

If EMF and Voltage are not same, but why using same SI unit for both?

Volt is the SI unit of both the EMF and the voltage. Rizosome (talk) 05:58, 16 October 2021 (UTC)[reply]

Voltage is the unit for Electromotive force. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:04, 16 October 2021 (UTC)[reply]

In both cases the quantity can be defined as the amount of work on a test charge moving in an electric field, so they have the same dimension (specifically, M L²T⁻³I⁻¹). As you can read in our article Electromotive force, it can be measured in two-terminal devices as the voltage between the terminals, so naturally the same unit is used. --Lambiam 07:37, 16 October 2021 (UTC)[reply]

Anti-Stokes %.

What are some examples of things that have a highest % of anti-Stokes? Like most emissions is like 95% Stokes, 5% anti-Stokes. What phenomenon have some of the highest percentage of anti-Stokes? 67.165.185.178 (talk) 12:16, 16 October 2021 (UTC).[reply]

Are you talking about Stokes shift? ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:05, 16 October 2021 (UTC)[reply]

Plant identification

Hi, I have described these as "cycads". Can anyone just check and confirm this, or even provide a species or more specific type name? ITookSomePhotos (talk) 16:27, 16 October 2021 (UTC)[reply]

Aren’t these just small palm trees? Here they are described specifically as date palm trees. --Lambiam 21:29, 16 October 2021 (UTC)[reply]

(edit conflict) I think jubaea chilensis or Chilean wine palm is a likely candidate. This article has a picture of a similar one growing happily on a traffic roundabout in London. Ventnor Botanic Gardens on the Isle of Wight has avenues of the things, according to this article, whose collection of Arecaceae have been given National Plant Collection status and says that warmer weather since the 1970s has made the island a good home for palms, most types of which normally struggle with the British weather. The most common palm seen here in southern England is the hardy Cordyline australis or cabbage palm from New Zealand, but these ain't they. Alansplodge (talk) 21:39, 16 October 2021 (UTC)[reply]

Silly me. I'll rename it. ITookSomePhotos (talk) 07:50, 17 October 2021 (UTC)[reply]

October 17

How a bird touching two wires would electrocute it?

I discovered that a bird touches two wires at once, it will create a circuit — electricity will flow through the bird and likely electrocute it.

How a bird touching two wires would electrocute it? I understand there is no ground between two wires, net potential differences is zero then how current flows through bird? Rizosome (talk) 02:41, 17 October 2021 (UTC)[reply]

Here's an explanation:[1] ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:46, 17 October 2021 (UTC)[reply]

It's very unlikely that two overhead electricity cables (assuming that's what you mean by wires) will be close enough for a bird to come in contact with both of them at the same time. But there is normally a big potential difference between adjacent cables (see Three-phase electric power) so they have to be kept apart so that the wind cannot cause them to come into contact and cause a short circuit.--Shantavira|^{feed me} 08:28, 17 October 2021 (UTC)[reply]

One suspected cause of the Roc becoming extinct, along with the decline of its preferred food. Clarityfiend (talk) 20:26, 18 October 2021 (UTC) [reply]

That must be how Popeye subdued the Roc in his voyage to see Sinbad. He sliced and diced the cooked bird into small nuggets and then opened a restaurant where one could buy a piece of the Roc. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:20, 18 October 2021 (UTC)[reply]

This YouTube clip shows a very large number of birds on power lines that apparently make a circuit when they all fly off at once (at 2:35). Perhaps several birds are close enough together that the current can jump the gap? Alansplodge (talk) 15:56, 19 October 2021 (UTC)[reply]

Tens of thousands to hundreds of thousands of birds are estimated to be electrocuted annually. Wildfires are sometimes started by electrocuted big birds catching fire (suggested web search: bird causes fire power line). A bird does not even need to touch two wires; flying close enough can make high voltage spark through air.

There indeed is a voltage difference between wires - otherwise what would be the point of having more than one wire. Distribution networks usually have at least two wires, though single-wire earth return installations exist mostly in remote areas.

There are a lot of things to unpack on this topic, depending how you imagine how things like "ground" work in electricity distribution. 85.76.79.135 (talk) 16:15, 19 October 2021 (UTC)[reply]

October 18

Inconsistency on Tesla Coil harming humans

I discovered that from wiki media, a Tesla coil producing high-frequency current that is harmless to humans, but lights a fluorescent lamp when brought near it. But here, it says Tesla Coil can harm humans. Which is correct? Rizosome (talk) 05:16, 18 October 2021 (UTC)[reply]

The risk is strongly related to the power output of the Tesla coil, and the frequency also plays a role. If the power is sufficiently low, a high-frequency Tesla coil will be harmless. --Lambiam 06:35, 18 October 2021 (UTC)[reply]

A fluorescent tube requires very little current.[2].--Shantavira|^{feed me} 08:30, 18 October 2021 (UTC)[reply]

The OP's question is a bit like asking "I heard that getting shot with a bullet is harmful to humans, but I touched a bullet and didn't die". The level of harmfulness is dependent on the energy transferred. A fast moving bullet shot from a gun is much more dangerous than, say, the same bullet thrown lightly from your hand. In the same way, the amount of energy imparted by the tesla coil to a person will have a big effect on how harmful it is. --Jayron 32 13:39, 18 October 2021 (UTC)[reply]

Switching from some genes to different ones as the organism matures

I know there should be a mechanism to activate some genes at certain stages of development. What is it?: AboutFace 22 (talk) 13:31, 18 October 2021 (UTC)[reply]

See Epigenetics and Regulation of gene expression for some introductions to the process. --Jayron 32 13:37, 18 October 2021 (UTC)[reply]

October 19

What's the cause of short circuit in this circuit?

In electrical devices, unintentional short circuits are usually caused another conducting material is introduced, allowing charge to flow along a different path than the one intended.

If another conductor is introduced then it makes circuit series connection, then what causes short circuit? Rizosome (talk) 01:24, 19 October 2021 (UTC)[reply]

Who says it does? What circuit are you talking about? There's an infinite number of combinations. Give us something to work with. --OuroborosCobra (talk) 02:05, 19 October 2021 (UTC)[reply]

Ummm... the conductor you introduced? The conductor has a (relatively) low resistance so the current will bypass the intended path of the current - essentially taking a shortcut i.e. the "short" circuit. 41.165.67.114 (talk) 05:58, 19 October 2021 (UTC)[reply]

It says here Rizosome (talk) 02:29, 19 October 2021 (UTC)[reply]

That section does not mention a "series connection". The cause of a short circuit is always the appearance of a new low-resistance parallel connection in the circuit. --Lambiam 07:49, 19 October 2021 (UTC)[reply]

Particle creation

In subatomic reactions which involve creation of particles, e.g. when stuff is smashed together at very high energies, is it known or believed whether the creation of these particles is truly instantaneous, or whether there is a finite (presumably incredibly short) formation period? — Preceding unsigned comment added by 2A00:23C8:7B08:6A00:F0CC:7064:9880:EDB7 (talk) 10:38, 19 October 2021 (UTC)[reply]

Such a thing may be unknowable. According to the uncertainty principle, certain measurable properties, known as Conjugate variables, cannot be simultaneously known to the same level of certainty. One of those conjugate pairs is "The energy of a particle at a certain event" and the " time of the event" that produced that particle are such a conjugate pair. If we know with high levels of certainty, the amount of energy of said particles, what we cannot know to any real certainty is when the event occured. It's not a technological limitation, it's baked into the mathematics of quantum physics. --Jayron 32 17:13, 19 October 2021 (UTC)[reply]

Leibniz asserted that "no transition is made through a leap",^[3] and I suspect most physicists, including quantum physicists, also hold this to be true. The idea of truly instantaneous change involving some spatial extension is fundamentally at odds with the theory of relativity. And, inasmuch as particles are excitations of some field, they have spatial extension. --Lambiam 18:53, 19 October 2021 (UTC)[reply]

October 20

Various types of honey

Living in the Western United States I purchase my honey at Amazon. It is collected in a Utah farm, It is a thick honey but this honey never crystallizes. Once upon a time I happened to travel to rural Utah for a reason different than collecting honey and in a small grocery shop bought a jar of honey. "Closer to nature" was my motivation. This honey crystallized two month after staying home. What's the difference between the two honeys? Is crystallized honey somehow not as good as the fluid one? Perhaps the one I purchase on Amazon is specially diluted with water to prevent crystallization? I feel there is a lot of mystery in my honey. Thanks AboutFace 22 (talk) 00:56, 20 October 2021 (UTC)[reply]

Our honey article talk about several factors that can affect crystallization, including the nature of the honey itself, temperature/handling, and addition of other ingredients. DMacks (talk) 05:34, 20 October 2021 (UTC)[reply]

[Edit Conflict] Honey (a natural and inherently variable substance to start with) can be processed in various ways, resulting in greater or lesser tendencies to crystallize (which is in itself not a problem: gentle heating will re-liquify it). Such variations in honeys do not make one or another inferior, just different.

Our article Honey discusses this at Honey#Classification by packaging and processing and elsewhere. {The poster formerly known as 87.81.230.195} 90.193.128.151 (talk) 05:38, 20 October 2021 (UTC)[reply]

It may also be worth noting that an enormous amount of honey is fake/adulterated/diluted (ref, ref). Matt Deres (talk) 15:03, 21 October 2021 (UTC)[reply]

How to know if a certain food contans caffeine (or any similar substance?

Dry food / fresh food / liquid food,

Is there any way to find if the food contains any "detectable" amount of caffeine (preferably doable at home)? Thanks 2001:44C8:4200:4FF2:16EA:EFA7:4BD4:A829 (talk) 03:44, 20 October 2021 (UTC)[reply]

Relatively inexpensive (say $10-20) Caffeine Test Strip Kits (easily websearchable) can be purchased, but these are intended to check that "decaffeinated" coffees and teas do not have excessive caffeine levels, or to roughly measure caffeine levels in drinks that are supposed to contain it. They would probably not be capable of detecting traces of caffeine in other comestibles that ordinarily do not contain caffeine in significant quantities.

Kits for detecting caffeine in breast milk (which may reach levels of around 1% of the level in the mother's ~~milk~~ blood) are or have been also available, and might be usable on other liquids.

More sophisticated and sensitive tests seem to require laboratory-level equipment such as spectrometers. Perhaps other editors may know of other means. {The poster fomerly known as 87.81.230.195} 90.193.128.151 (talk) 05:26, 20 October 2021 (UTC)[reply]

"Detectable" is a question of how you choose to try to detect it--different methods have different lower-limit of detection. So an HPLC system might find a very low level (ppm), whereas a test-strip might only find a few tens of mg per serving-size. It's pretty easy to extract the caffeine from a few tea-bags or coffee-grounds using kitchen chemistry and materials from a local hardware store, and it's sensitive enough to find that different brands/styles of coffee have different content. But it is not easily generalized to "any food" (coffee is a fairly simple combination of chemicals) and obviously depends on how good a balance or scale you have. But if your goal is just "does it contain?" then you don't need to quantify, just observe. DMacks (talk) 05:49, 20 October 2021 (UTC)[reply]

Can HPLC have selectivity to detect a compound as large as caffeine? I thought the instrumentation in biology labs are more suitable for this? Eliza? 67.165.185.178 (talk) 11:10, 21 October 2021 (UTC).[reply]

Depends on the matrix. Caffeine is a pretty small molecule even in the simple-structures organic world, let alone in the world complex and large biomolecules. There's lots of literature for using it to detect caffeine in blood, quantitative validation down to tenths or hundredths of a microgram per mL even without resorting to a mass-selective detector (LC-MS). DMacks (talk) 11:51, 21 October 2021 (UTC)[reply]

If all else fails, consume a significant quantity late in the evening and see if it keeps you up that night. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:32, 21 October 2021 (UTC)[reply]

Article Cited by Anti-Vaxxers as Evidence COVID-19 Vaccines Are Not Effective.

This article, Increases in COVID-19 are unrelated to levels of vaccination across 68 countries and 2947 counties in the United States seems to go against the scientific mainstream that COVID-19 vaccines are effective against the spread of COVID-19. Am I misunderstanding something? Has this article passed peer-review? A Quest For Knowledge (talk) 15:52, 20 October 2021 (UTC)[reply]

It doesn't go against anything. It's a data point, and a true one from what I can tell. However, it doesn't mean what you say it means. It doesn't mean that vaccination is not an effective strategy for stopping the spread of disease; rather it likely shows that no place has reached a high enough vaccination level yet. The highest vaccination levels it quotes are 75%... That's not high enough to see the effects they are looking for. What we have seen is that at the same time that vaccination levels are rising, other methods have been entirely abandoned (distancing, reducing travel, masking, etc.) so that any positive effect we would be getting among vaccinated people reducing transmission has been more than offset by the negative effect caused by all of the unvaccinated people abandoning prophylactic measures designed to stop transmission. If we want to know if vaccination is effective, we need to compare transmission rates among fully vaccinated people with those who are not vaccinated at all. This study throws all of these people together in one giant pot and doesn't isolate vaccination status as a single variable, since other factors (all of the prophylactic measures I noted above) are also changing at the same time. Rule #1 of conducting a valid experiment is to isolate your variables. --Jayron 32 16:03, 20 October 2021 (UTC)[reply]

Published in a reputable journal. The header says "correspondence", but I do not know where it fits within the "types of article" journal page. Whichever peer-review occur must have been light, considering the authors used data from September 3 and the article was published on September 30 (the delay between data collection and submission to journal, and the delay between submission of the first draft and publication, is usually several months across most scientific disciplines). This being said, even with proper peer review, the most outlandish things have been published in the best journals (example).

I can add a few methodology remarks to Jayron32’s. Taking a single point in time is not serious - possibly the authors have been sitting on the analysis script for three months until the daily data agreed with their proposed narrative.

Furthermore, they assert that their selection criteria were that the dataset on ourworldindata.org had second dose vaccine data available; had COVID-19 case data available; had population data available; and the last update of data was within 3 days prior to or on September 3, 2021.) If you go and look at the country list in their supplementary file (btw, great job using a word document to hold a data table, guys) it looks quite weird. China is not included (but Russia is, so it is not a case of "potentially fabricated data so we exclude it"), France is not included (I supposed based on the "last update" criterion because looking at the page right now all the rest are met).

Finally, I see no honest reason to present the vaccination rate vs. recent cases differently in figure 1 (world data) and figure 2 (US counties). I clearly see a dishonest reason: even on figure 2, looking at the center lines, you can see a downward slope, i.e. a correlation that goes against their narrative; the bins and whiskers are just here to obscure it. (This is IMO the biggest point that a reviewer should definitely have caught if peer review had been done properly.) I also suppose (but cannot know because the supplementary information does not contain the actual excel file) that their correlation line in figure 1 was drawn with assigning a weight of 1 to every country, though obviously a weighting by population would be more appropriate. Tigraan^{Click here for my talk page ("private" contact)} 10:19, 22 October 2021 (UTC)[reply]

I agree with both Jayron32 and Tigraan above: too many hidden variables (eg. population density, political alignment, anti-infection measures, level of social cohesion and public compliance, population age distribution, income distribution, latitude, temperature and weather, you could go on and on...), far too little statistical analysis, and I don't think it really proves anything one way or the other. It would be interesting to see some more detailed research into the matter. -- The Anome (talk) 10:33, 22 October 2021 (UTC)[reply]

October 21

Why Lights go dimmer even current increases?

Voltage drops occur when loads are increased and also an increase in current occurs. Lights that are on the same circuit to appear dimmer. Why they go dimmer ?Rizosome (talk) 04:42, 21 October 2021 (UTC)[reply]

What is the context in which you found these statements? Voltage drop occurs across any load. The statement does not make much sense; it is similar to "Gravity occurs when weights are increased". What is the circuit? The current may increase in one branch while decreasing in another branch. Does the current increase in the branch with the light source? --Lambiam 06:48, 21 October 2021 (UTC)[reply]

It says here: As load current increases, the voltage drop in the wiring increases and the voltage delivered to the system drops. Rizosome (talk) 17:36, 21 October 2021 (UTC)[reply]

Take a circuit with two components in parallel. One component has a variable resistance, say an electric heater with an on–off switch. The other is a light bulb. Label the two end points of this parallel circuit A and B. This circuit is connected in series with a constant resistor (representing the resistance of the wiring) with end points B and C. The two ends of the combined circuit, A and C, are connected to a source with a constant voltage. There are two paths for electricity to flow: between A and B either via the variable resistance or via the light bulb, and then between B and C via the resistor. Assume the variable resistance is initially infinite (the heater is switched off). All current flows through the light bulb. Now assume the heater is switched on, so the resistance in its branch goes from infinite to fairly low. The combined resistance of the parallel part of the circuit, and therefore that of the whole circuit, then drops considerably. So now a much higher current flows between A and C, and therefore via the resistor between B and C. The voltage between B and C therefore increases, and that between A and B drops by the same amount. Therefore the current through the light bulb decreases. But in this new situation there is a strong current through the parallel branch with the heater. The sum of these two currents is higher than before. --Lambiam 20:05, 21 October 2021 (UTC)[reply]

Can you give me circuit diagram of this bulb and electric heater? Rizosome (talk) 05:12, 22 October 2021 (UTC)[reply]

See here. For simplicity I have indicated the constant-voltage power source with the symbol for a battery, but the story is the same for an AC source as for DC. --Lambiam 13:13, 22 October 2021 (UTC)[reply]

Do cetaceans hear in the air

Cetaceans have peculiar auditory system evolved specifically for underwater hearing. Does it mean that they are completely deaf when out of water (for example, when stranded ashore or when they are transported in hammocks)? Эйхер (talk) 16:40, 21 October 2021 (UTC)[reply]

NOT A RELIABLE SOURCE, but this says that they can. --Jayron 32 16:47, 21 October 2021 (UTC)[reply]

It is well known that cetaceans being in water are able to hear sounds produced above the water. For example, dolphin trainers routinely use whistles for cueing dolphins. But it is usually assumed (or at least, assumed by some trainers) that in this case the sound passes from the air into the water. I mean the case when the animal is completely out of the water. For example, do dolphins, when transported by plane in hammocks, suffer, like terrestrial anumals (including humans), from the noise, or they rather suffer from dead silence? Эйхер (talk) 05:08, 22 October 2021 (UTC)[reply]

The acoustic properties of a dolphin aren't too dissimilar to those of water. If the sound can pass from air to water, it should be able to pass directly from air to dolphin. Most of the sound will be reflected though. The whole purpose of the middle ear in terrestrial animals like humans is to transfer the sound from gas to liquid without too much reflection. PiusImpavidus (talk) 08:24, 22 October 2021 (UTC)[reply]

The problem is that, as far as I can understand (being not a biologist), cetaceans have degenerate middle ear with disfunctional ossicles and rely instead on bony hearing, that is enhanced in them through some sophisticated adaptations. Эйхер (talk) 13:09, 22 October 2021 (UTC)[reply]

Industries that need electrical power just for part of the day?

Are there any industries that need reliable electricity, but can tolerate having it for only part of the day [not just day-night!] because it can shut down and up with little difficulty? I am thinking things like Chloralkali process. JoJo Eumerus mobile (main talk) 16:47, 21 October 2021 (UTC)[reply]

"Industry" is very broad. We got along just fine before electricity came along. Industries that don't rely on electricity include Commercial fishing, most types of Agriculture, Haulage, Forestry, the Military, most forms of Transport, many divisions of the Construction Industry, and Tourism.--Shantavira|^{feed me} 08:34, 22 October 2021 (UTC)[reply]

Well, yes, to some extend. With the rise of intermittend, clean energy sources like wind and solar, we need such industries that can adapt their usage to the available electricity. Some industries can rapidly adjust their power use and production rate to available power. Completely shutting down may be a bit much. Aluminium smelters are one example. When electricity gets expensive, they shut down some of their electrolysis cells, just supplying them with enough power to keep the contents molten. Not using the factory at full capacity at all times takes money, but they recuperate this with on average cheaper electricity. Clean hydrogen production is another one. Storing energy in hydrogen isn't very efficient, but if you only make hydrogen when energy is free, it may pay off. PiusImpavidus (talk) 08:36, 22 October 2021 (UTC)[reply]

@PiusImpavidus: Aye, I was wondering about aluminium smeltering and electrolysis. Out of curiosity, do you have any sources that discuss these aspects? Jo-Jo Eumerus (talk) 10:13, 23 October 2021 (UTC)[reply]

Doctor House and Bipolarism

In the episode Failure_to_Communicate, we saw a person, who has a bipolar disorder. The amazing thing is that the patient is manic during the day and sleeps off his depression at night. Is this account plausible? A bipolar disorder that changed within one day?--2A02:908:426:D280:D82B:8A4C:3F13:8022 (talk) 18:38, 21 October 2021 (UTC)[reply]

I have not seen the episode, but our article states that the patient is thought to have been using amphetamines during the day and sleeping pills at night. Amphetamines are a dopaminergic stimulant of the central nervous system that can induce euphoria similar to a manic state, so it seems plausible to me that in the logic of the plot the patient took both forms of self-medication, day and night, to counter symptoms of depression. --Lambiam 10:37, 22 October 2021 (UTC)[reply]

Thermodynamics question

Suppose that the inside of a house is initially at the same temperature as the outside. A heat pump is then used to raise the inside temperature by some given amount. This uses x amount of supplied energy to drive the heat pump. A heat engine is now employed to extract work from the inside-outside temperature difference, and this produces y amount of mechanical energy. Is the minimum possible x equal to the maximum possible y? Please note that this question is about theoretical limits under laws of thermodynamics, not about what can be achieved practically. 109.147.111.142 (talk) 20:59, 21 October 2021 (UTC)[reply]

No. Impossible. One of the consequences of the Second law of thermodynamics is that the processes you described will never occur with 100% efficiency - some of the energy supplied to the pump and the engine will be unavailable and will leak into the surroundings in the form of heat at a low temperature. Dolphin (t) 21:09, 21 October 2021 (UTC)[reply]

The fact that not all the heat energy inside the house can be recovered in usable form is incorporated into the question as an essential part of it. 2A00:23C8:7B08:6A00:BC7D:139D:88FE:38A5 (talk) 21:23, 21 October 2021 (UTC)[reply]

See Carnot's theorem and Carnot cycle. Эйхер (talk) 21:16, 21 October 2021 (UTC)[reply]

I am aware of those articles. It is beyond me to figure out the answer to my question from this. 2A00:23C8:7B08:6A00:BC7D:139D:88FE:38A5 (talk) 21:32, 21 October 2021 (UTC)[reply]

Assume your heat pump is the best theoretically possible. It runs at Carnot efficiency. The heat pump does not increase entropy, so it's reversible. So you can run your heat pump in reverse without decreasing entropy, and you get exactly the heat engine you use to extract work from the temperature difference. So, indeed, the minimum work you need to run the heat pump equals the maximum work you can extract with the heat engine. PiusImpavidus (talk) 08:43, 22 October 2021 (UTC)[reply]

(edit conflict) Yes (almost). Per Coefficient_of_performance#Theoretical_performance_limits: At maximum theoretical efficiency, [the ratio of transferred heat to work for a heat pump] is equal to the reciprocal of the ideal efficiency for a heat engine (thus the product of the two efficiencies is close to 1). The paragraph also gives a short derivation (the "it can be shown that..." part is a consequence of Entropy#Reversible_process).

Of course, that is only with a perfect heat pump and a perfect heat engine, so the actual performance will not reach that. The table at Heat_pump#Performance indicates that actual heat pumps reach about 25% of the maximum efficiency. I am not sure what the situation is for a plausible heat engine in the context of the question, but surely it must be worse than power plants that from my memory^{[citation needed]} reach 1/2 to 2/3 of Carnot efficiency. The total yield on one cycle (y/x in the terms of the question) would be around 10-20% with those numbers, quite far from 100%. Tigraan^{Click here for my talk page ("private" contact)} 09:23, 22 October 2021 (UTC)[reply]

Let me clarify one important point implied in the question by selecting a few representative temperatures. Let's assume the temperature outside and inside is a uniform 10°C. The heat pump produces air at 30°C and this air enters the house, raising the inside temperature by "some given amount". Let's assume that given amount is 10°C so the temperature inside the house rises to 20°C. Some responders to this question have assumed that the heat engine would have access to air at 30°C. However, the question appears to be based on the heat engine only having access to air from within the house which is at a significantly lower temperature than 30°C. This indicates another reason why the proposal is impossible. Dolphin (t) 10:57, 22 October 2021 (UTC)[reply]

Well, if the system experiences no heat losses, then the air temperature inside becomes asymptotically close to 30°C, and given sufficient time, will be immeasurably close to 30°C; which is to say given an arbitrarily long length of time, the inside temperature will reach our target temperature to within the limits of our measurements. --Jayron 32 11:17, 22 October 2021 (UTC)[reply]

When you blow 30°C air into a 10°C room, the mixing is irreversible, so entropy increases and the efficiency must be less than Carnot efficiency. For maximum efficiency, you take air from the room, make it infinitesimally warmer with heat pumped from outside and blow it back into the room. The Carnot efficiency is the limit, which you can approach arbitrarily closely, but in reality, you rarely get anywhere near. But then, OP asked about the theoretical limits, not what can be achieved practically. PiusImpavidus (talk) 14:48, 22 October 2021 (UTC)[reply]

Thanks a lot for the replies. Here in the UK, heat pumps are very prominent in the news right now. While I have read numerous explanations about how these work on a practical and even theoretical basis, I have found no explanation anywhere that helps one gain any intuitive understanding of how on earth it is possible to get more energy out of a heat pump than one puts in when the outside temperature is colder than the inside. Per my comment at Talk:Heat_pump#Suggestion_for_improvement, it seems rather like pumping water uphill and finding that one has gained more energy than one has supplied. If the answer to my original (self-devised) question is yes, then, for me, this is the first glimmer of understanding about how heat pump >100% "efficiency" may be possible. In my scenario, not all the heat can be recovered from the house as usable energy, which I understand, and so if the process is (theoretically) reversible then it must imply that the house can be heated with less energy than the resulting heat energy in the house. However, I think that this observation may not be very helpful for most people. Anyway, if anyone has any bright ideas how to address my comment at Talk:Heat_pump#Suggestion_for_improvement, I think it would be to the benefit of that article. 2A00:23C8:7B08:6A00:F55B:27D8:6291:2C56 (talk) 21:59, 22 October 2021 (UTC)[reply]

I think the answer to your question is that the heat pump in that scenario is using a different heat reservoir than you're imagining. A Ground source heat pump can be a source of heat (or cool!) even in situations when the outside air is not the right temperature.

If you go far enough below the frost line, the ground temperature is basically the year-round average temperature. In many places, that's ideal for a heat-pump. ApLundell (talk) 04:45, 23 October 2021 (UTC)[reply]

That doesn't seem to be answering the question. Air source heat pumps are getting increasingly common, both for heating internal air but also for heating water in large part due to climate change concerns. In countries with mild temperatures (e.g. UK [4], France [5] [6], Germany [7], Australia [8] [9] [10], NZ [11] although our articles notes they are useful even in the Yukon on Canada with temperatures down to -30 °C with the right heat pumps), they do use less electricity than a simple electrical resistive heater, generally one of the key reasons they are getting more popular.

To be clear, electric resistive heaters directly convert electricity into heat at close to 100% efficiency (of the electricity which reaches them not from the PoV of production) so the fact heatpumps generally use less electricity is I think the source of the OP's confusion as it is for a lot of people. And they are nearly always used when the outside temperature is cooler than the outside or reverse if being used to cool the air inside i.e. to increase the temperature difference. As water heaters, the temperature differential is generally even greater. Ground source hear pumps would generally use even less electricity to produce the same heating (or cooling) effect but the high price of installation and maintenance means in a lot of countries especially those with mild temperatures and for installation in existing buildings, they're still rare or at least far less common than air-source ones.

There is some concern of their increase electricity use. One is because for internal air heaters, they will be used in reverse direction i.e. to cool the air during summer whereas in the past most people would have just used fans and ventilation so this leads to an increase electricity use during summer even in cases where their adoption leads to a decrease during winter. The other because in many countries they are not being used to replace electric heaters but instead some form of combustion heater. But for the latter, the desire is that the country will produce enough of their electricity by renewables or other forms of generation that don't contribute significantly to increased emissions of greenhouse gases.

The first part of an answer to the question seems to be the OP is misunderstanding what a heat pump is doing. Despite the fact you are moving more heat than you could produce via a simple resistive heater, from a cooler outside to a warmer inside, it's not accurate to say you are producing more energy then you put into the system. Probably next part is to remember that even air source heatpumps are moving heat from or to effectively a massive reservoir as it's not just the air outside the structure that's the source of the heat.

Nil Einne (talk) 07:56, 23 October 2021 (UTC)[reply]

"confusion" is not a fair word to use in respect of my post, nor is there any "misunderstanding" as to what the heat pump is doing. "get more energy out of a heat pump than one puts in" is just somewhat loosely worded: I don't mean more energy overall, in the whole Universe. I am well aware that the extra is moved from the outside. The difficulty is in understanding how this is possible when the outside temperature is colder. I don't understand how the outside being a "massive reservoir" helps to explain this. Common responses to questions about this are inability on the part of the responder to understand the question, and/or mistaken assumption that the person asking the question has made some blindingly simple error of understanding about what is going on. I wish we could get past these stumbling blocks and onto the actual point. In response to the earlier reply, whether the outside source is air, ground or water is completely irrelevant. 2A00:23C8:7B08:6A00:AA:B98:8E44:3013 (talk) 09:45, 23 October 2021 (UTC)[reply]

Many people, including me, have wondered how a heat pump works exactly, and how it is possible to move x joules of thermal energy from a lower temperature to a higher temperature without having to expend the same amount (x joules) of electrical energy, little realising that most of us already own a heat pump called a refrigerator! A refrigerator takes x joules of heat from the cold storage space and pumps it out into the kitchen where it slightly raises the temperature of the air inside the kitchen. (That small rise in temperature of the air in the house is a nuisance in the summer but slightly beneficial in winter.) A conventional heat pump does the same thing except that instead of taking heat from a small enclosed cold storage space it takes it from the environment. Both a refrigerator and a conventional heat pump raise the temperature of their working fluids to a bit above room temperature in order to discharge heat into the interior of the house, thereby raising the temperature inside the house. Dolphin (t) 12:52, 23 October 2021 (UTC)[reply]

As far as the oft-repeated refrigerator analogy is concerned, please see my comment at Talk:Heat_pump#Suggestion_for_improvement. 2A00:23C8:7B08:6A00:15E5:2AA5:F4D3:2978 (talk) 19:04, 23 October 2021 (UTC)[reply]

A heat pump is not like “a refrigerator in reverse”. Thermodynamically it is exactly like a refrigerator. I will think about your request at Heat pump and make a suggestion. Dolphin (t) 21:25, 23 October 2021 (UTC)[reply]

October 22

Calculating the apparant location of the Moon(altitude/azimuth)

I'm writing a program to calculate the altitude and azimuth of the Moon as seen from a given location at a given time. I've translated the BASIC code on this page: http://www.stargazing.net/kepler/moon.html to Delphi. )I found an error or two.) I get it to agree with his sample of Birmingham, UK on August 9, 1998. His calculations agree with those of Mooncalc by Monzur Ahmed (given on that webpage).

However, he uses these figures for the latitude and longitude of Birmingham:

   lat : -1.91667
  long : 52.5

which are reversed. In his program glat and glong are used for the viewer's latitude and longtitude.

Question 1: are glat and glong reversed in his program?

Question 2: To convert from Right Assention and Declination to Altitude and Azimuth, it asks for the Hour Angle. Is that simply the number of degrees of longitude? Bubba73 ^{You talkin' to me?} 01:35, 22 October 2021 (UTC)[reply]

Well, I thought to put in the time of today's moonrise. With the lat and long as written, the data doesn't make sense. If I flip them, then I get 1.0 degrees altitude, 81.5 degrees azimuth for the time of today's moonrise, according to the weather report. Azumuth is 8.5 degrees north of east, which is reasonable. It gives the altutude at 1 degree, when it should be 0. His program is supposed to have a maximum error of 0.3 degrees. Bubba73 ^{You talkin' to me?} 02:29, 22 October 2021 (UTC)[reply]

Hour angle. Sagittarian Milky Way (talk) 03:59, 22 October 2021 (UTC)[reply]

The article says "... measured westward along the celestial equator from the meridian to the hour circle passing through a point." But the example the author gave, westward is negative. Is that inconsistent with the convention? Bubba73 ^{You talkin' to me?} 04:50, 22 October 2021 (UTC)[reply]

I have software where Earth's eastward rotation AKA the 1 westward spin of the celestial sphere per day adds to the hour angle, same direction as the article. The hour angle of the Sun is local actual (not mean) solar time in hours p.m (12 hours out-of-phase with 24-hour time, but the astronomical and nautical day are also 12 hours after or before the regular day), it would be weird if time counted down. Right ascension also ascends, not counts down (unless something is moving retrograde but retrograde orbits are cleaned from solar orbit in only millions of years so they're not that important). Sagittarian Milky Way (talk) 21:32, 22 October 2021 (UTC)[reply]

Webster's Dictionary also says westward Sagittarian Milky Way (talk) 13:56, 23 October 2021 (UTC)[reply]

Risk decrease of masks

When a COVID-19 patient (A) and an uninfected person (B) spend some time together, there is a certain risk of transmission. It may decrease if one or both wear surgical mask. The decrease can be expressed as a percentage. There are three situations: only A wears a mask, only B wears a mask, both A and B wear a mask. Article Face masks during the COVID-19 pandemic mentions percentages but does not distinguish situations. Has this been researched and percentage estimates published? Thank you. Hevesli (talk) 04:11, 22 October 2021 (UTC)[reply]

If anyone can answer that question with reliable information, it would be nice to add it to Face_masks_during_the_COVID-19_pandemic#Efficacy_studies_for_COVID-19. I cannot, so what follows is speculation.

I would assume no such research exists for covid19. A response study (asking A and/or B purposefully not to wear masks when it is known that A is probably infected) would be highly unethical with a disease that severe. I imagine it is hard to design a proper observational study (if you ask people who have been around sick people who wore masks when, the chance of lying/misremembering is fairly high). This being said, such studies might have been done for other diseases that could be used as models of transmission (e.g. common cold coronavirii). Tigraan^{Click here for my talk page ("private" contact)} 09:40, 22 October 2021 (UTC)[reply]

An evidence review of face masks against COVID-19 (Jan 2021) says:

Cochrane [12] and the World Health Organization both point out that, for population health measures, we should not generally expect to be able to find controlled trials, due to logistical and ethical reasons, and should therefore instead seek a wider evidence base. This issue has been identified for studying community use of masks for COVID-19 in particular. Therefore, we should not be surprised to find that there is no RCT for the impact of masks on community transmission of any respiratory infection in a pandemic.

Alansplodge (talk) 10:26, 22 October 2021 (UTC)[reply]

Just as an aside: this year's (2021) Prize in Economic Sciences (commonly called the Nobel Prize for Economics) was awarded to laureates who showed how to use "situations in which chance events or policy changes result in groups of people being treated differently, in a way that resembles clinical trials in medicine"; the prize was specifically awarded for solving "this methodological problem, demonstrating how precise conclusions about cause and effect can be drawn from natural experiments." In other words, when it is not possible or ethical to conduct a proper random control trial, there is still a valid methodology to draw conclusions with equal scientific rigor. It happens that this methodology is "difficult," which is why the prize was awarded to a few scientists who "totally revolutionised the way we do empirical work."

Guido Imbens even wrote an entire book titled Causal Inference for Statistics, Social, and Biomedical Sciences. The book offers "unprecedented guidance for designing research on causal relationships, and for interpreting the results of that research appropriately." This sounds verbose, but I would endorse it. We don't want a simple "yes" or "no" on whether masks decrease the risk of transmission: we need a nuanced and careful methodological approach to this question. It is this nuance - particularly, distinguishing scientific methodology from hollow weasel-wording - that I believe justifies the award; and, simultaneously, is what implies that you need a book-length answer to a question that initially sounds like it deserves a simple binary-answer.

Nimur (talk) 17:43, 22 October 2021 (UTC)[reply]

October 23

Question on Brush in DC motors.

How do brushes change polarity in DC motor? By changing polarity, torque produced, hence shaft rotates on its axis Rizosome (talk) 00:07, 23 October 2021 (UTC)[reply]

The following graphics illustrate a simple, two-pole, brushed, DC motor.

DC motor rotation

A simple DC electric motor. When the coil is powered, a magnetic field is generated around the armature. The left side of the armature is pushed away from the left magnet and drawn toward the right, causing rotation.

The armature continues to rotate.

When the armature becomes horizontally aligned, the torque becomes zero. At this point, the commutator reverses the direction of current through the coil, reversing the magnetic field.

The process then repeats.

--84.190.201.130 (talk) 01:17, 23 October 2021 (UTC)[reply]

The magic happens in the Commutator (electric). That article explains it rather better I think.--Shantavira|^{feed me} 08:22, 23 October 2021 (UTC)[reply]

Or the OP could more simply read the caption to the 3rd diagram, where the question is answered.--Phil Holmes (talk) 09:31, 23 October 2021 (UTC)[reply]

Why does LiDAR have the ability to see depth through mirrors?

Hi all.

Recently got a new phone, and it has a LiDAR camera on it. I've noticed, however, that when looking at the pure depth information from it, it has the ability to see the depth of objects beyond mirrors (almost as if you flipped the room using the mirror's plane as the axis of symmetry). Why is this? I thought mirrors reflect light, not depth...? Or is it simply the mirror just reflecting the LiDAR rays?

I've taken a picture of my bathroom mirror to highlight what I'm referring to.

DrawWikiped^(talk) 21:36, 23 October 2021 (UTC)[reply]