Recently when I was procrastinating, I have learned that an electric energy is not propagated via wires but through fields. Once a circuit is closed, a field is created and it carries the energy from a source to eg a light bulb. It proposed a question to me.
The question is, how does the current/source know that the circuit has been closed?
Let’s ask two similar questions, both assume ideal conditions.
1. we have a source and a switch on Earth and a light bulb on Mars. We close the circuit using the switch and the energy starts to be emitted from the source in an almost instant. After some time, once the field reaches the bulb, it starts to emit light.
2. we have the same situation, but the switch is moved to Mars. Will it take the same time for the bulb to emit light? How does the source know that the circuit has been closed and it can start to emit and electric field?
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Well first off, energy is transfered through wires, and in power electronics the fields are more of a byproduct. In your earth/mars scenario it would take the same amount of time regardless. The thing is that the source dosent “know” anything. Electrons will only flow if there is a big enough potential difference. So if you just stick one end of a wire in space, chances are that the ambient potential is very close to your ground. Once you connect a device that is at a much higher potential (usually the other side of the battery/generator) the electrons start to flow and take time to arrive (slower than speed of light). But you also have to differentiate between DC and AC current, as AC currents can also carry signals and different waveforms in the fields produced by the oscillating electrons. But speed is still the same.
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