Wikipedia:Reference desk/Archives/Science/2023 May 7

= May 7 =

Domestic appliances
In ovens, washing machines, coffee machines etc. (at least those that I've needed to fix), it seems that the various heaters, motors and actuators have one terminal connected to the live rail, with the switches, thermostats and controllers on the neutral side. Why's it that way around? catslash (talk) 00:32, 7 May 2023 (UTC)


 * Live rail? Do these appliances run on tracks? Perhaps there is a rationale grounded in the theory of electricity, but I suspect this is an arbitrary convention, just like the colour codes of wires are an arbitrary convention. --Lambiam 09:56, 7 May 2023 (UTC)
 * I assume the use by User:catslash of the expression “live rail” is just a local variation on what Wikipedia calls a busbar. Dolphin ( t ) 14:42, 8 May 2023 (UTC)


 * In electrical devices I've taken apart here in Canada, if the "hot" and "cold" wires could be distinguished then the switch was always on the hot side. Perhaps Mr. Catslash should identify what country the devices he or she is talking about are from. --174.89.12.187 (talk) 04:45, 8 May 2023 (UTC)
 * Indeed. I am not an electrical engineer (I can wire a plug and that's about it), but I'm fairly sure that in the UK this is a legal requirement under The Regulations. {The poster formerly known as 87.81.230.195} 90.213.18.208 (talk) 12:51, 8 May 2023 (UTC)
 * The regs apply to installations. The OP is asking about individual appliances which will be subject to some sort of type approval. Martin of Sheffield (talk) 14:21, 8 May 2023 (UTC)
 * Do they not also apply to appliances? I know that the Electricity at Work Regulations 1989 necessitate workplace portable appliances in the UK being regularly tested, and I'm also sure that imported appliances have to be manufactured to certain safety standards. What different standards are those? (The answer doesn't really matter to me, but might be relevant to the OP.) {The poster formerly known as 87.81.230.195} 90.213.18.208 (talk) 18:44, 8 May 2023 (UTC)
 * Yes, there are regulations for any appliances placed on sale in, or imported into, the UK. It's just that the wiring regs aren't the appropriate regulations.  The old name (under the IEEE before BS took them over) was "Regulations for the Electrical Equipment of Buildings" and as the name suggests covered wiring (cable types, protection etc) protective devices (consumer units and the industrial equivalents) outlets, switches, grounding, equipotential bonding and half a dozen other things that I can't remember.  They didn't cover equipment downstream of the socket outlet or equivalent switchgear.  For instance the regs cover the installation of the cable up to a cooker switch, but not the internal wiring of said cooker.  Likewise the regs cover ring mains but not the TV you plug in. Martin of Sheffield (talk) 22:13, 8 May 2023 (UTC)
 * The question concerns the inner workings of appliances in the UK, but typically manufactured in other European countries. It does not relate to the main on/off switch, if any, which would be on the "hot" side. catslash (talk) 22:16, 8 May 2023 (UTC)
 * cooker example catslash (talk) 23:02, 8 May 2023 (UTC)

Eagle's brow ridge
Eagle_eye says the bony brow ridge "protects the eyes from protruding tree branches when it perches on trees, and also from prey which struggles to escape". Considering that some other birds of prey and generally many other animals live in a similar tree habitat and have similar hunting behavior, why that bony ridge evolved only in eagles? Apparently there are similar adaptations elsewhere that for some reason are not present among all genera living in the same habitat and sharing similar behavior. 212.180.235.46 (talk) 17:14, 7 May 2023 (UTC)


 * The process of genetic mutation is basically random, but mutations that happen to be beneficial tend to be selected for preservation in what is basically a process of optimization by trial and error. It is therefore entirely possible that one branch in the phylogenetic tree, by sheer luck, hits upon an improvement while nearby branches for which the same change would also be beneficial are less lucky. The counterpart of this is convergent evolution, in which somewhat distant branches occupying similar niches hit upon the same or similar improvements in the struggle for reproductive success. --Lambiam 18:48, 7 May 2023 (UTC)
 * I don't think there is any reason to believe the sub-par sources that claim a protective function for the brow ridges. They could just as well be sexually selected, or to cut down on glare when hunting over water, or to keep water out of the eyes, or have no function at all. Abductive  (reasoning) 07:18, 8 May 2023 (UTC)