Facebook – energy flow in circuits, collisions, earth, moon

Gauthier Östervall The mechanisms by which energy moves in solids, liquids, gas, mixtures solutions, structures all depend on the details of what you are doing. I am reviewing “shock vaporization” and “shock melting” this morning. It mainly affects meteor impact melting and vaporization but also hypervelocity flight, reentry, weapons development, explosive compression and forming, magnetic shock experiments. But in each of those very real instances, there is no simple one step answer, and almost never is it a one person process. I saw a video early today about an experiment that had 10,000 authors — because it took coordination and effort by that many.

In regard to your question about flow of current in wires or channels.  Generally people ignore the microscopic details and focus on the measurement of voltage and current over time, do the impedance calculations for simple inductance capacitance resistivity (or conductivity) and use that data for something else.  It makes it hard for someone who wants to focus on how energy flows in solids, but what happens is people jump over how it works and just go as fast as they can to using electricity and magnetism to study other things or to make stuff happen.

Generally the discussions I read all end up saying the electrons move fairly slowly, because there is one electron per atom in copper, and the molecular weight of copper is about 63.546 grams per mole. The density of copper is about 8.96 grams/centimeter^3. So (63.546 grams/8.96 grams/centimeter^3) = 7.0922 milliliters (cm^3). So you get a mole (6.022E23 atoms) in a cube of copper that is (7.0921875 cm^3)^(1/3) = 1.9213 cm on a side. There are 96485.32 Ampere Seconds per mole, so it takes many seconds to move that many Coulombs of electrons at 1 Coulomb/Second = 1 Ampere.

Many circuits now use milliAmperes, and microAmperes. I work on problems routinely that use GigaAmperes, TeraAmperes and larger. Those I use Moles of charge per second. I also have problems where Kilograms of electrons or MegaGram (a metric ton) of electron charges are needed.

Google will do a lot for you but they are flaky and unreliable. It might work one day and not the next. If you “search” for

(Avagadro’s number)* (electron mass) it will give you 548.579909 microGrams for the mass of a mole of electrons.

A Kilogram of electrons would be (1 kilogram)/((Avagadro’s number)* (electron mass)) = 1,822,888.49 moles of electrons.

It is hard to find the precise visual models for conventions for all the fundamental constants and things like “electrons”. You sort of have to put your hopes on hold and just take it a step at a time. It took me 45 years to find a decent mass for the graviton, and thousands of hours of tedious checking.

Not sure if that gives you some hints, but that is the way I think about electrons in wires, in material, in molecules. I do think about and use concepts like “pulsing all free electrons in the earth” and “pulsing and removing all electrons from an atom” and “removing all electrons from the neutrons of a nucleus”. Those always take some degree of “art”. But eventually one finds something satisfactory, or you got to other problems, depending on your purpose and goals in life.

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Richard Collins, The Internet Foundation

Gauthier Östervall The electron has a charge. The electrons move, their charge moves. Because there are so many electrons in wires, each electron on average only has to move a little and slowly for the currents observed to occur. It is millimeters per second. The term is “drift velocity” Ask “How fast do electrons move in copper” and you will get examples of what people find. A good but complicated explanation is at https://en.wikipedia.org/wiki/Speed_of_electricity

In semiconductors the holes matter, at high frequencies the energy is stored and moved in fields. It is a messy area of research. I mostly do not look at the velocity of the electrons unless they are specifically emitted and can be timed. What is more important (to me anyway) is the energy transferred. And that is measured in Watts or Watts/Meter^2.

If you have a particular thing you are trying to do, it is easier to figure that out, than to try to understand all the many things millions of people have worked on over the last few centuries. I have about 60 text books on electromagnetism on my shelf, and that many chemistry books at least. All of chemistry can be done by looking at charges and fields. But it is not organized to use easily. So what I do is take each problem and try to understand it at the time I tackle it. Some of the things I have worked on for many decades. Some things are not done. Some things I will die before I ever find out. Life is interesting, it is not ever completely clear what matters, if at all. Today I worked on how to correct the light that comes from the regions near black holes and neutron stars. And this afternoon it was aerosols, dust, and things in the atmosphere interacting with light from the sun and heat from the earth and clouds and air. If you go outside and look at things, just a glance you can see many hundreds of things. Each one there are millions of people around the world that try to understand them — but mostly everyone works alone, there are few standards or common tools. Somehow the human species as a whole seems to survive and things sometimes creep along and things get better for a few.

Yes that speed of electricity article on wikipedia is good, but not easy. There are problems that can be answered in minutes, there are problems that take hours. Some that take years, and I mostly work on those that take individuals many decades, or many people working together many years.