Diana Lamb

2022-10-05

At what speed does electric information go?Consider a parallel circuit with each branch of equal resistance. If you increase the resistance of the further branch, how long would it take to detect that from the intersection (since (the majority of the) current takes the path of least resistance)?

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Electric information is electromagnetic information. It travels at the speed of light in the medium in question. In vacuum this is c, but in circuits it is somewhat less (but still very fast). The different resistance follows the same general rule.
The speed of light for a circuit is a little more complicated since the circuit acts somewhat like a waveguide and waveguides have non-trivial signal propagation characteristics. One of the simplifying assumptions of circuit theory is that the distances and frequencies involved are such that the electromagnetic information can be assumed to propagate instantaneously. If that assumption is violated then using circuit theory is unlikely to produce accurate results.

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