Wikipedia:Reference desk/Archives/Science/2021 May 6

= May 6 =

Butterfly ID requested
Yesterday my father told me that when taking his afternoon walk in North San Jose/Milpitas, he saw a butterfly which he is sure was a swallowtail (he described its shape as "strictly triangular", which in my experience is only ever seen in swallowtails and very rarely in nymphalids), but rather small by swallowtail standards (he estimated its wingspan at about 2 inches, or as he said it was "about the size of a cabbagefly") and with a solid yellow coloration (like a brimstone butterfly) with no tiger stripes. I think it could have been an anise swallowtail (and told him as much) -- can anyone verify? 2601:646:8A01:B180:A990:90F3:3BA2:4FBB (talk) 01:38, 6 May 2021 (UTC)
 * A colour abberation that extreme seems unlikely to me (though I'm not saying it's impossible). I think it more likely that it was a normal specimen of an entirely different species (perhaps even a day-flying moth – I first thought of the Brimstone moth, but realised it's not found in the Americas). As I'm really only familiar with British, and to a lesser extent European, lepidoptera, someone from the US will be better placed to suggest possible candidates: nothing obvious in List of butterflies of North America or the family articles linked from there jumps out at me. I would note that due to climate change, many species are beginning to be seen beyond their previously normal ranges, so maybe check out List of butterflies of Mexico in case there's something that's made its way in there but not to the NA list. {The poster formerly known as 87.81.230.195} 90.200.135.95 (talk) 13:40, 6 May 2021 (UTC)
 * OK, so can anyone familiar with North American butterflies verify? And BTW, here's something which might be relevant: from time to time (and especially in the summer of 2017), I've seen butterflies of a similar description in the San Jose area -- swallowtails (I'm 100% sure they're swallowtails, I've seen the hindwing spurs, which are rather long and prominent) with narrow sharply-pointed forewings, about 2 1/2 inches across (i.e. about the size of a red admiral and too small for my old "friend" Papilio rutulus, much less the dreaded P. multicaudata), and from a distance they look almost completely yellow (except that the rearmost part of the wings is black, including the spurs, and there is a little bit of black on the leading edge too, but no tiger stripes like those of P. rutulus) -- so the question is, might these be the same as the one my father saw? 2601:646:8A01:B180:4418:4F68:23D:D201 (talk) 06:22, 7 May 2021 (UTC)
 * Never mind -- I saw this critter just this afternoon, and the size estimate given was way off (I estimate it as about 3 1/4 to 3 1/2 inches, or about twice the size of a cabbagefly), so I've positively identified it as a Papilio rutulus (and a fair-sized one at that) -- and yes, it did actually have tiger stripes, just not very visible from a distance! 2601:646:8A01:B180:C02F:4D92:1D13:D06D (talk) 01:44, 8 May 2021 (UTC)

Are there any difference between capacitors and batteries?
Capacitor stores electric charge. Isn't that same thing battery stores? Both are storing energy in a form of electricity. Rizosome (talk) 14:54, 6 May 2021 (UTC)
 * I would look at battery and capacitor. While capacitors do store electric charge, batteries do not. Batteries generate a potential difference (voltage) through redox chemical reactions at an anode and a cathode. They do not store "electric charge," but rather have potential energy due to their non-equilibrium state. — Preceding unsigned comment added by OuroborosCobra (talk • contribs)

Does removing capacitor from circuit will make any difference in current flow? Does circuit consume more voltage than before? Rizosome (talk) 18:27, 6 May 2021 (UTC) The main difference between batteries and capacitors is that the voltage across a capacitor is proportional to the charge it holds, whereas the voltage of a battery is approximately constant until it's almost depleted. I suppose you can treat the reciprocal of the slope of the voltage-v-charge curve as being the battery's "effective capacitance" in some sense, though I wouldn't be surprised if the slowness of the chemical reactions made that a not-so-useful thing to do for a lot of purposes.
 * Capacitors have a lot of different uses (see Capacitor) and if there is one in your circuit, it is there for a reason, removing it will have deleterious effects on whatever device it was in, usually. Electrical systems are finicky, and just yanking devices out willy-nilly is likely to go badly.  In terms of the effect of the capacitor on the flow of electricity (i.e. on the voltage and current in the circuit), it's complicated, but if you want to dig into it, you can get all of the details at Capacitor.  The actual voltage drop across the capacitor has a lot to do with the specific design of the capacitor and the design of the rest of the circuit.  -- Jayron 32 18:57, 6 May 2021 (UTC)
 * I think electrolytic capacitors split the difference in some sense. --Trovatore (talk) 19:45, 6 May 2021 (UTC)
 * I wonder if the OP still doesn't understand the difference between velocity and acceleration? (Or for that matter, the difference between speed and velocity.) ←Baseball Bugs What's up, Doc? carrots→ 21:23, 6 May 2021 (UTC)

I understand pretty well, capacitor and batter are almost equal. Both stores electrical energy but in a different way. Rizosome (talk) 00:14, 7 May 2021 (UTC)
 * No. Batteries do not store electricity. --OuroborosCobra (talk) 15:19, 7 May 2021 (UTC)
 * Now that that issue is settled, we need Rizo to explain the difference between speed and velocity. ←Baseball Bugs What's up, Doc? carrots→ 22:25, 7 May 2021 (UTC)
 * With batteries, more capacity is usually better: they last longer. That's why alkaline batteries have largely replaced carbon-zinc ones. With capacitors, bigger is only better when they are being used to store energy, to smooth the output of a rectifier for example. In most applications, capacitors aren't used to store energy, but to block (attenuate) or pass (amplify) signals above or below a certain frequency, or to oscillate at a certain frequency, and that frequency depends on the capacitance: a higher capacitance takes longer to charge and discharge, so the frequency is lower. The capacitor in the tuning circuit of a transistor radio for example determines the tuning frequency, change it and you receive a different station (most variable capacitors used in tuners have a maximum capacitance below 1 nF, less than one millionth of a typical smoothing capacitor). The high-pass RC (resistor-capacitor) filter in a loudspeaker protects the tweeter by blocking the low frequencies. In oscillators, increasing the capacitance will lower the frequency...  Prevalence  02:49, 7 May 2021 (UTC)

Side comment: In the Canadian TV series Murdoch Mysteries, set in the late 19th and early 20th century, the title character is a detective who very much enjoys science. There's a scene in one episode where he is telling an audience of police officers about an incident where a man was electrocuted by a Leyden jar, an early type of capacitor. Told that a capacitor stores electricity, one of the officers says "So it's a kind of battery, then." Murdoch says no, and the next thing, he's finding it necessary to explain the difference... --184.147.181.129 (talk) 07:39, 7 May 2021 (UTC)

My question only on electricity not signal processing. Rizosome (talk) 18:00, 8 May 2021 (UTC)
 * A capacitor is nothing more than two metal plates with an insulator between them. Charging it means moving electrons from one plate to the other. The plate that has lost electrons is positively charged (has more protons than electrons), the other one is negatively charged. The more electrons you move, the harder it gets: it becomes more diffult to remove electrons because the positive charge attracts them, it becomes more difficult to add them to the other plate because the negative charge repels them. So the voltage goes up (because that's the definition of voltage: the amount of work needed to move a charge). A charged capacitor carries a static electric charge (static because it's not moving). If you short ( = put a metal conductor between the two leads) a charged capacitor it will discharge in an instant, often with sparks flying (those aren't electric sparks, but tiny pieces of white hot metal caused by the high current melting and evaporating the metal at the point of contact). A capacitor can release most of its charge in microseconds, the rate is only limited by the resistance and inductance of the plates and the wires.
 * A battery doesn't store charge, it stores energy in chemical bonds. The anode and cathode form a capacitor with a very small capacitance, and the battery keeps that capacitor charged. If you take away charges (discharge the battery), the voltage drops, the lower voltage between anode and cathode causes the battery to generate more charges (electrons) to raise it again. If you apply a higher voltage to the battery, the extra charge is converted into chemical energy (charging the battery).
 * When you short a battery (connect the + to the - side), a current will flow until the battery is fully discharged (the time it takes depends on the battery type, from a few minutes to several hours).
 * A battery can hold much more energy than a capacitor. A non-electrolytic capacitor the size of an AA battery would have a capacitance of at most a few hundred µF. A 470 µF capacitor charged to 1.5V has a charge of 0.0007 Coulomb (the equivalent of 4.4*1015 electrons), a NiMH AA battery with a capacity of 2300 MAh can deliver 8300 Coulomb (or 5*1022 electrons), 11*106 times more.
 * A mechanical analogy would be: a battery is like a compressor running on gasoline, it can deliver compressed air at a pressure of 16 bar until it runs out of fuel. A charged capacitor is like a cylinder with compressed air at 16 bar: it can deliver much less air than the compressor, and the pressure only starts at 16 bar, it will have dropped to zero by the time the cylinder is empty. But (with the right valve) the cylinder can release the air it contains almost instantly, the compressor would take seconds or minutes to deliver the same amount.   Prevalence  18:25, 9 May 2021 (UTC)
 * I applaud your detailed answer,, but it is wasted effort. --OuroborosCobra (talk) 18:34, 9 May 2021 (UTC)

decomposite each taste to 5 tastes of humans
It is known that most of human taste is made of just 5 base tastes. I wonder why can't we represent each taste as combination of those tastes, like we do with base colors? And like color, composite each taste by using only 5 base chemicals?--Exx8 (talk) 23:49, 6 May 2021 (UTC)
 * You not only taste food, you also smell it. Without the smell food tastes very bland. (It has been said that if you plug your nose, you can't tell the difference between the taste of an apple, an onion or a raw potato https://www.huffpost.com/entry/without-sight-or-smell-apples-and-onions-taste-the_b_595d40d8e4b085e766b50fd4 ). So to recreate the taste, you would also have to recreate the odor, which is more difficult: we have about 400 different olfactory receptors, each of them activated by a range of different molecules (odors), and one odor will activate several different receptors. So you would have to find a mix that activates the same receptors in the same amount as the food does..  Prevalence  03:18, 7 May 2021 (UTC)


 * The decomposition of vision by three base colors is grounded on the fact that (most) humans have three types of color-perceiving cells. Things are more complicated for taste: from our article, The basic [five] taste modalities contribute only partially to the sensation and flavor of food in the mouth — other factors include smell, (...) texture, (...) temperature, (...) and "coolness" (...) and "hotness" (pungency) (.... Tigraan Click here to contact me 08:40, 7 May 2021 (UTC)
 * As noted, there's a distinction to be made with the "five main tastes" of sweet, sour, salty, savory (umami), and bitter that are detected directly by the tongue, while "flavor" generally includes the entire sensation of eating, which includes contributions from smell and touch as well (see mouthfeel); the subjective flavor of food can also be affected by vision and mood as well; famously the color of a food will affect how a person describes its flavor, even where the color itself has no effect on taste or smell. -- Jayron 32 16:30, 10 May 2021 (UTC)