[Answer] When Does Current Begin to Flow After an Extremely Long Circuit Is Closed?

[Answer] When Does Current Begin to Flow After an Extremely Long Circuit Is Closed?

If a circuit were as long as a light-year, that would probably only have logical or theoretical significance.

In the common analogy that compares electric circuits to water pipes, closing a switch is roughly like opening a sluice gate. If there is a difference in water level on the two sides of the gate, opening it causes water to start flowing. Likewise, if there is a potential difference across the two terminals of a switch, closing it causes current to flow.

In a purely theoretical discussion, just as water flow begins at the gate itself, I think the current should first appear at the switch rather than at the power source. The potential difference across the switch would produce current there first, and if the circuit were long enough, that current would gradually propagate back toward the power source.