Science desk
< November 11	<< Oct \| November \| Dec >>	November 13 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is a transcluded archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

November 12

Mechanical hierarchy - fixing appliances.

Q1. When it comes to HVAC, PTAC (fixing air conditioners, central air), is there a hierarchy for most-roundedness? I personally think fixing microwaves is the most well-rounded, especially if you also know how to fix washing machines. So if you know how to fix microwaves, it should be easy to learn how to fix something else?

Q2. I'd also like to know what's 2 different fields with low-overlap? For example, someone who is an electrician, does not know how to fix ovens. And someone who fixes ovens, does not necessarily know how to be an electrician? So if you train to fix ovens and an electrician, not much overlap?

So, to summarize, Q1 = someone who can fix A, can fix A and B, but someone who can only fix B, does not know how to fix A. Would microwaves be a good candidate? And Q2 = A and B do not overlap. Thanks. 67.165.185.178 (talk) 03:59, 12 November 2021 (UTC).[reply]

The term "fix" has too broad a meaning to answer this. Let's stay with the microwave. Fix it by replacing the broken turntable belt. Sure. Easy. Fix it by repairing a blown circuit board with your soldering iron - not so much. By "fix" do you mean replace a faulty component with a part you found on ebay or do you mean taking your multi-meter and oscilloscope any diving into the guts and diagnosing the the faulty component on the circuit board, remove a chip or blown capacitor and solder a new one in? 41.165.67.114 (talk) 06:56, 12 November 2021 (UTC)[reply]

Sounds like your definition of fix is the same, just a matter of components and intensity. But you could take this to the farthest level: someone who knows how to build a microwave from scratch, and this write tutorials on how it works and how to assemble 1. So, going back to my analogy, I take it people who can fix microwaves, can fix toasters, but people who only know how to fix toasters, would not know how to fix a microwave? 67.165.185.178 (talk) 12:42, 12 November 2021 (UTC).[reply]

Someone who can fix a microwave whose turntable stopped rotating by replacing a broken belt may be totally helpless with a toaster that stopped working or causes a short circuit. No one in their right mind is going to build a microwave from scratch. Today, any class of appliances requires specialized expertise. The owner of an appliance may be out of luck anyway when it stops working for some trivial reason – many are designed so as not to be fixable for a cost less than that of a complete replacement. It is somewhat pointless to seek to define a hierarchy. --Lambiam 13:40, 12 November 2021 (UTC)[reply]

Yes, but isn't there a principle where if you can fix the circuit of a __, then you can also fix the circuit of something else? Is what I'm looking at. And therefore familiarity with what to replace. 67.165.185.178 (talk) 14:06, 12 November 2021 (UTC).[reply]

If the "something else" is really something else, and not a more specific instance, you'll be hard-pressed to find a non-trivial example. In these days of integrated circuits and mass assembly, an all-round electronic technician will generally not be able to fix any circuit other than replacing it wholesale. They may be able to diagnose and understand the problem, but that will do them little good in fixing it. --Lambiam 14:21, 12 November 2021 (UTC)[reply]

Sure, "more specific instance." Don't appliances have these in common? So if you know how to replace 1, you can replace it in a different appliance. 67.165.185.178 (talk) 14:27, 12 November 2021 (UTC).[reply]

"What did you say your specialty is?" — "I am a fully licensed RX 6700 XT replacer." --Lambiam 13:12, 13 November 2021 (UTC)[reply]

Ah, repair, repair, a topic I love so very much...

I think there do exist specific contexts where there are strictly defined hierarchies: environments fraught with rules, regulations, ratings, and certifications...

In an environment like a medical laboratory, a military unit, or an aviation-related industry, specific repairs are enumerated, tracked with paperwork, and are permitted to be performed only by authorized and appropriately trained individuals. (Whether any particular person or organization complies with those rules is out-of-scope, for this discussion).

One example that I am specifically familiar with pertains to aviation. The ambitiously-named "Part 43 - Maintenance, Preventive Maintenance, Rebuilding, and Alteration (also known as Title 14 C.F.R. Chapter 1 Subchapter C Part 43) lays out some rules. § 43.3, "no person may maintain, rebuild, alter, or perform preventive maintenance" ... (unless that person complies with the rules and regulations so verbosely defined). And how verbosely, exactly, is that? Well, Appendix A of this part defines what things count as "major repairs", "major alterations," and so forth. This list is literally on the test. It is not only a dumb idea, it is almost always illegal to perform those repairs except in strict compliance with the rules.

In the aviation industry, mechanics and repairmen are clearly defined: they are individuals who have been trained and tested, and hold appropriate certificates and ratings, § 65.1. The maintenance and repair work they perform is authorized, itemized, inspected, and logged. So, the bit about fixing microwaves: is the microwave attached to an airplane? If yes, there is mandatory paperwork associated with its repair! And am I simply blathering about a bunch of nonsense, as usual? Absolutely not : there really are really real reasons to be concerned about the microwave that's attached to your airplane, and you want to know that the person fixing it is qualified.

Paperwork to the rescue!

For medical devices, military equipment, and so on, you can bet that there are similar rules, regulations, and paperworks. I don't happen to be so intimately familiar with those rules, and I haven't memorized them, but along those same lines, medical people have strict rules about which people can do which tasks, sorted by which trainings and certifications and current experience requirements those people meet. Are these "hierarchies?" Well, not strictly: a doctor can do a superset of tasks that a nurse may perform, and a nurse may perform a superset of tasks compared to a Paramedic, or an EMT, or a phlebotomist, or an Ambulance Driver, and so on down the so-called hierarchy; but there are things that a technician is trained to do that a doctor is not trained on. It would be a good idea for the doctor to delegate such tasks to the trained individual, rather than pulling rank and pretending to know how to do it "better." Here is a lovely introduction from the FDA: Remanufacturing and Servicing Medical Devices: The distinction between "remanufacturing" and "servicing" is important to understand. How can one not fall in love with this degree of Government specificity? I wish everything in engineering was so well-specified!

For consumer goods like household appliances - in the home setting - one probably doesn't consult the paperwork for every type of repair; but generally, consumer products lay out those items of service that should be performed only by an authorized service-provider; such repairs can be certified (a word that I love very much, because carries so much more grammatical gravitas than the word we use to describe aircraft repair operations, e.g. "work performed by a certificated individual"). Those rules are there for a variety of reasons - legal liability, cost, safety, ... consumer satisfaction (... the manufacturer probably knows more about the device than the consumer, and knows that a shoddy "DIY" at-home-repair can make a broken device into a more broken device, which on the average makes the consumer less happy). There are a lot of elements in the mix. Many users today claim that modern "devices" (at large) are "difficult" to repair, and some make the further claim that such difficulties are "on-purpose" (rather, "restrictions" implemented or encouraged by the device manufacturer). A well-balanced view is warranted: sometimes, such claims are valid; sometimes, such claims are not valid. These issues show up in the news, and in popular electronics- and consumer-products- websites - a lot. It is my personal opinion that most of the inflammatory rhetoric on this topic doesn't really contribute much factual information. So:

For a fun read on the topic of Repair, here's a very recent (May 2021) book: An FTC Report to Congress on Repair Restrictions, which gives a pretty solid introduction to some of the items of concern.

Nimur (talk) 15:32, 12 November 2021 (UTC)[reply]

Capacitor questions.

Q1. A capacitor stores electrical energy in an electric field. How can we measure a fully charged capacitor? Is there devices that do that?

Q2. How do we get electrocuted from touching capacitors? Is it from touching their dielectric component?

Q3. It seems all texts distinguish capacitors from parallel-plate capacitors. Are there any common household appliances, that use both capacitors and parallel-plate capacitors? Or do most devices, just use 1 type?

Q4. "Any 2 electrodes, regardless of shape, form a capacitor." Well electrodes are conductors. What if the 2 electrodes were semiconductors, then what kind of a capacitor would 2 semi-conductor electrodes be called?" Thanks. 67.165.185.178 (talk) 19:15, 12 November 2021 (UTC).[reply]

2. From short circuiting them with your body. Some capacitors can electrocute you just from putting fingers too close, or falsely show full discharge on measuring devices then partially recover enough to electrocute again. Sagittarian Milky Way (talk) 23:22, 12 November 2021 (UTC)[reply]

1: A multimeter or any other device that measures voltage.

3: Textbook parallel plate capacitors have a rather small capacitance. Maybe very small values (picofarad range) ceramic capacitors might be plain two plates. Usually the plates are wrapped to a roll, or there are many layered plates. See capacitor types or search the web/youtube for capacitor teardown.

4: A diode. Usually diodes are constructed to minimize their capacitance as it is generally undesirable, but varicaps are used specifically for their capacitance. 85.76.74.133 (talk) 11:14, 13 November 2021 (UTC)[reply]

I generally think of the electric field as in air, so I don't know how a digital multimeter can measure it. 67.165.185.178 (talk) 13:25, 13 November 2021 (UTC).[reply]

A charged capacitor has a voltage differential between its wires. A multimeter can measure that voltage. If you want to measure the energy in a capacitor, you need to discharge it through a resistor of some kind and measure current and voltage and integrate the product of those over time. If you are a visual learner, go to YouTube and search for e.g. measure capacitor voltage to see people test capacitors. While there, supercapacitor might find interesting stuff. 85.76.74.133 (talk) 15:57, 13 November 2021 (UTC)[reply]

Wait does electrocution from capacitors also include from parallel-plate capacitors? 67.165.185.178 (talk) 17:40, 14 November 2021 (UTC).[reply]

Do human lungs have more protection against smoke compared to other animals?

Our ancestors have used fire for more than a million years. Wood smoke is not good for the lungs, but our ancestors were depended on fire. Especially in colder regions of the World like in Europe, where people would have been sheltering in closed spaces like caves or tents, the exposure to smoke would have been significant. I've been in Arctic regions and been inside tents used by indigenous people. They use woodstoves inside tents, and while there is a chimney, the concentration of smoke inside is huge. After a while your eyes start to burn.

So, the question is whether after tens of thousands of generations living in such conditions, our lungs have evolved to neutralize the damage done by wood smoke to some degree? Count Iblis (talk) 22:56, 12 November 2021 (UTC)[reply]

Yes, and moreover I have heard that dogs heal faster from burns on their paws and mouths than wolves. Abductive (reasoning) 21:49, 13 November 2021 (UTC)[reply]