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MercurianAspirations t1_jedzagy wrote

Reply to comment by femmestem in ELI5: How are we able to direct narrow bands of magnetic fields like utility lines if Earth's magnetic field emanates outward from the core towards the atmosphere? by femmestem

I still don't understand what you mean - it's the current flowing through the conductor that is going from power station to a residence, not energy in a field

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PerturbedHamster t1_jeeic9v wrote

Yeah, OP is actually correct that it's the field. If you have say a 700 kV power line, that means the voltage difference between the two lines is 700 kV. The laws of E&M mean that there has to be an electric field between the two lines, so if you took a charged particle from one line to the other, it would pick up a ton of energy. Incidentally, this is why working on high voltage lines is kind of intense, and the lines themselves have to be incredibly smooth (I think surface imperfections are micron scale or smaller to avoid coronal emission). It's the electric current moving through the field, both of which are provided by the generating station, which carry the energy. It's easy to forget that Maxwell's equations still apply to transmission lines, but they do!

To answer what I think is OP's question, classical magnetic fields don't do any work because the force is always perpendicular to the direction of motion, so the Earth's magnetic field doesn't do anything for power transmission. The Earth doesn't have a large scale electric field, because ions in the atmosphere would rapidly adjust to cancel it out. There aren't a lot of ions in the lower atmosphere (and again, transmission lines are very carefully designed to not create new ones), so the electric field doesn't get cancelled out and we can send power down the lines.

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femmestem OP t1_jef4th6 wrote

This makes a lot of sense, thank you! I'm not specialized in physics, just a curious layman who learned about fields and then had a "hey, wait a minute..." moment. You made this explanation very accessible to me.

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PerturbedHamster t1_jefn2sx wrote

Glad you found it useful! You might enjoy looking at pictures of corona emission from power lines, which really let you see how strong the fields next to power lines are. The fields get so strong that they just rip electrons off of atoms, and you can see the glow as they combine back together. Wikipedia has some nice pictures here.

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