Wikipedia:Reference desk/Archives/Science/2023 February 18

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February 18

Tuna fins and scales

Wondering whether tuna were kosher, I ran a Google search and found blurbs from sites saying that some varieties are, and some aren't. However, I've tried to load several such sites, and either they won't work (maybe they don't like my IP address?), or they don't appear to answer the question...so I come here instead. Are there big differences from one tuna species to another, to the point that some species don't meet the basic kosher requirement of "fins and scales"? Or are all species rather similar, and the kosher status depends on some smaller aspect of Jewish law? Nyttend (talk) 01:51, 18 February 2023 (UTC)

It could depend on what they feed on. For example, as I understand it, catfish are not kosher because they are "bottom feeders". ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:25, 18 February 2023 (UTC)

Well, that's one of those "some smaller aspect of Jewish law" things. [Next sentence sounds like a complaint, but it's not.] I came here, not RDH, because I wanted to ask about the tuna-anatomy issue instead of halakhic interpretations. Nyttend (talk) 03:44, 18 February 2023 (UTC)

According to this article,[1] tuna are considered kosher. The issue seems to be in the preparation of them. With canned tuna, it can be uncertain whether kosher laws were followed in the preparation. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:00, 18 February 2023 (UTC)

[Edit Conflict] Tuna and the individual species linked from it will have a good deal about the anatomy of the 15(-ish) species, but you probably knew that. Skipjack tuna seems to be the species with fewest (but not no) scales. {The poster formerly known as 87.81.230.195} 51.198.55.125 (talk) 07:06, 18 February 2023 (UTC)

Here is an informative article about tuna species and their scaliness, which has a considerable variation between species. The scales of a fish need to be discernible by the unaided eye for it to be considered having scales in halakhic law. This disqualifies several tuna species. Eels also actually do have scales, but since you can't see them, they are not kosher.  --Lambiam 15:04, 18 February 2023 (UTC)

Do microwaves need to be calibrated over time?

Microwaves give off 2.45 GHz radiation, from the magnetron. What would cause it to have some failure where it starts giving off slightly different radiation, like 2.46 or 2.44 GHz? Should microwaves even need to be calibrated over time? Weird trivial question lol. 67.165.185.178 (talk) 14:18, 18 February 2023 (UTC).

The frequency of a microwave is the resonant frequency of the arrangement of the cavities of its magnetron, which is determined by their physical dimensions. Since the magnetron consists of a large, solid cylinder of metal in which cavities are drilled, one would need an extraordinary force to deform it so much that these physical dimensions undergo an appreciable change. After it has been run over by a steam roller, one's microwave may be in need of calibration – but if it is still operating, albeit at a slightly different frequency, like 2.46 or 2.44 GHz, one need not worry – these frequencies will do the job just as well.  --Lambiam 15:15, 18 February 2023 (UTC)

Magnetron frequency drifts for a number of reasons:

• The load on the magnetron (frequency pulling); the operating frequency is a resonance of the whole system, consisting of the magnetron cavities and the external circuit (the oven cavity, the food and any mode-stirrer). The arrangement of the external part is by design randomized by rotating the food and/or mode-stirrer.
• Temperature; the frequency drops as the anode heats up and the cavities expand.
• The current through the magnetron (frequency pushing); the presence of electrons in the magnetron changes the resonant frequency.

Even if the magnetron can be considered as a perfectly isolated and empty cavity, there exist an infinite number of resonant modes with different frequencies. The wanted mode is the π-mode, where alternating individual cavities oscillate in antiphase. However, when the magnetron is switched on or off, the applied voltage may briefly be such as to allow the excitation of other modes.

For regulatory compliance, it is sufficient for the oven to operate at between 2.4 and 2.5GHz. catslash (talk) 19:16, 18 February 2023 (UTC)

The OP uses every-day speech "microwaves" to refer to a consumer Microwave oven. For safety these ovens are designed to leak (give off) least possible of their internal electromagnetic radiation intended to heat food. The internally generated frequency of nominal 2.45 GHz (wavelength of 12.2 cm 4.80 in) is not exact or stable because the low-Q resonant-cavity magnetron drives the poorly-matched food cavity that rotates the food to avoid uneven heating by persisting standing waves. This video shows frequency spectrum of stray emission of an oven. To allow for this variation the FCC allocates a 100 MHz bandwidth 2.40 to 2.50 GHz for ISM (Industrial, Scientific and Medical) use. Excessive radiation leakage in this range or any radiation outside the band are both avoided by design; the latter is important because there are nearby frequency allocations for mobile communications, including IMT-2000/UMTS, mobile satellite communications, weather/ship radar, Bluetooth, Wi-Fi, Zigbee and other technologies, see What is the S Band?. Philvoids (talk) 20:10, 18 February 2023 (UTC)

Transformers questions.

1. Transformers are to increase or decrease the voltage. Called step-up or step-down. Since voltage is inversely connected with current, then can we safely say transformers are also to increase/decrease the current? Yet no 1 seems to define it that way.

2. Transformers tend to have an oil fluid around it due to heat given off. As oil is heated, oil expands, and transformers have areas where oils can move into. So what causes more of heat, step-up, or step-down? (Voltage.). Thanks. 67.165.185.178 (talk) 14:22, 18 February 2023 (UTC).

(1) Transformers can also be 1:1 for isolation purposes. You're right in your assumption, in a perfect transformer Vin×Ain = Vout×Aout. (2) Transformers are unfortunately not perfect. Expanding the equation we get: Vin×Ain = Vout×Aout + Wloss The size of W depends upon many factors in the design of the transformer. W is dissipated as heat. See transformer for a more erudite explanation. Martin of Sheffield (talk) 14:31, 18 February 2023 (UTC)

Okay, so it looks more likely, a big increase in voltage/current are a big increase in heat given off, so either direction (step up or step down) will do. 67.165.185.178 (talk) 14:47, 18 February 2023 (UTC).

The length of the handles of a pair of pliers is connected with its gripping force. You can increase the force by extending the handles. You cannot extend the handles by increasing the force. Same with the voltage–current relation. Given the load, you can increase the current by increasing the voltage. You cannot increase the voltage by increasing the current.  --Lambiam 15:26, 18 February 2023 (UTC)

So if you increase the current, voltage is decreased? Where watts is still the same? 67.165.185.178 (talk) 18:20, 18 February 2023 (UTC).

Current is simply a measure of "flow rate". You cannot increase it without either (A) increasing voltage or (B) decreasing resistance, so it really doesn't make sense to talk about "increasing current" as if it were some kind a "tunable parameter" per se. Earl of Arundel (talk) 19:42, 18 February 2023 (UTC)

OK, here is a worked example. I'm going to assume that the transformer is perfect, that is has no losses. Clearly this is not true, but it keeps the explanation simple. Assume that there is a mains input and a 12V output with a 1.2 ohm resistor connected across the output. The output circuit will therefore draw 10A (from V=IR). This gives a Vout×Aout of 12 × 10 = 120 VA. To supply this we need Vin×Ain to also equal 120, therefore 240 × A = 120 or the current drawn from the mains socket is 0.5A. As Earl of Arundel points out, this is controlled by the 12V output and the 1.2Ω resistor. The transformer simply transforms the input and output so that 12 × 10 = 240 × 0.5. Martin of Sheffield (talk) 21:06, 18 February 2023 (UTC)

If you increase the resistance of the output the voltage will not change much but the current will decrease. This is why we think of it as changing the voltage. The maximum current one could have when reducing the resistance will be set by the supply and the size of the transformer. NadVolum (talk) 21:33, 18 February 2023 (UTC)

@NadVolum: but have you considered current transformers whose characteristics are such that the output voltage rises until the wanted current flows (within rather strict limits)? Martin of Sheffield (talk) 22:29, 18 February 2023 (UTC)

They are used for measuring current, there is no wanted current. NadVolum (talk) 11:30, 19 February 2023 (UTC)

Okay 1 thing I am stuck on, as current is the flow of charge. Which are electrons, and flow of electrons induce an electric and magnetic field. What if the particles were instead, protons? And you have proton-electricity. What kind of a field does that induce? And to make it more complex, protons are H+ ions. Which is synonymous with acid. So now it has a pH. ;d 67.165.185.178 (talk) 14:02, 19 February 2023 (UTC).

It would make no difference if the protons move in thw opposite direction to the electrons. The + and - of electricity were chosen at random before anyone knew about electrons, it would have made more sense to have had the electrons be + and be moving to the -. NadVolum (talk) 16:18, 19 February 2023 (UTC)

It would not be easy to create a flow of protons. Perhaps you mean positrons. See als Dirac hole theory. For the purpose of understanding conventional electric circuits, the magnetic component of the electromagnetic field can usually be ignored – but obviously not in the operation of transformers or electromagnets such as found in electric motors.  --Lambiam 17:10, 19 February 2023 (UTC)

Exactly. A proton is almost 2000 times more massive than an electron. Good luck pushing a single amp's worth through a conventional circuit. That said, it would be interesting to see if a coiled tube of flowing acid could generate any appreciable inductive effects (or say, a proton-powered solenoid). Earl of Arundel (talk) 18:43, 19 February 2023 (UTC)

Even with an electric stove working full pelt at home the electrons would only be moving on average somethng like half a millimeter a second. Pretty surprising when you consider how fast the lights turn on! NadVolum (talk) 20:14, 19 February 2023 (UTC)

The electrons in a circuit being closed start moving at (almost) the same time. It is not as if they are pushed forward by those behind them bumping into them.  --Lambiam 23:53, 19 February 2023 (UTC)

True. The electromagnetic field itself propagates throughout the circuit more or less at the speed of light. Earl of Arundel (talk) 19:23, 21 February 2023 (UTC)

Just as a data-point, GeV-range particle accelerators seem to be commonly generating proton beams of a few 10s of mA. That's not a bad way to cook a tumor, but pretty bad to make a pot of tea. DMacks (talk) 20:43, 19 February 2023 (UTC)

While some acids contains protons (as H⁺ ions), they contain an equal number of negatively charged conjugate-base ions that flow at the same rate in the same direction, so the net effect of flowing acid is not an electric current.  --Lambiam 23:50, 19 February 2023 (UTC)

Proton conductors do exist. There are also solid lithium ion (and other ion ) conductors, even including a silver ion conductor. Graeme Bartlett (talk) 07:52, 20 February 2023 (UTC)