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It doesn't really "generate" a field. The EM field is always there, permeating the universe. An acceleting electron will _disturb_ the EM field (depositing some
by amadsen 3y ago
It doesn't really "generate" a field. The EM field is always there, permeating the universe. An acceleting electron will _disturb_ the EM field (depositing some energy and momentum into it), and this disturbance will propagate through the field at the speed of light (naturally, since at the right energy level such a disturbance is what we call light). At high energies the disturbance will be finely localized in space and behave like a particle, which we call a photon. It's fine to refer to it as such also at lower energies, but slightly misleading because at the very low energies that we talk about here ("radio") it is very spread out in space and behaves more like a wave (with a wavelength of ~meters). In the case of AC, electrons are moving "back and forth" over a short distance (somewhat simplified but useful picture) with the same effect. Think about moving your hand up and down through water - you will create a wave.
- programmer_dude 3y ago>The EM field is always there Did you mean to say "the E field is always there"? Loved this explanation otherwise.
- computerfriend 3y agoIt's one field, which can be split into E and B components if you like.
- georgeg23 3y agoThe B field is just the E field's relativistic effects to an observer not in the same motion frame. https://wikipedia.org/wiki/Classical_electromagnetism_and_special_relativity https://wikipedia.org/wiki/Classical_electromagnetism_and_sp...
- H8crilA 3y agoBoth are always there if the circuit is running. Also, both E and M fields are required to transport any power using electricity. This is also true for DC current. See https://en.wikipedia.org/wiki/Poynting_vector https://en.wikipedia.org/wiki/Poynting_vector - the formula multiplies E by B, therefore if any of the two is zero no power (or information) transmission can occur. This is true over the air, as well as over a wire.
- rusk 3y ago>The EM field is always there Hmm sounds dangerously close to aether theory. I thought we had moved past this … that EM waves exist in their own right without need for a medium. Unlike sound say.
- gabia 3y agoAether refers to some historical ideas (which evolved over time), and though the word isn’t in use anymore the current model of fields has similarities (ofc in many ways very different). Have just been reading some of the history of this (Einstein plays a big role), it’s very interesting, thank you! :) You might be interested in this discussion https://news.ycombinator.com/item?id=27942970 https://news.ycombinator.com/item?id=27942970
- rusk 3y agoWay over my head unfortunately
- zmgsabst 3y agoWilczek points out that field theories are aether theories — as is relativity. “Aether just means this one particular historical model!” is branding more than reality; and hides the fact that modern theories also describe an everywhere substrate of which particles are localized excitations and gravity is localized warping.
- runlaszlorun 3y agoAir is aether.