I’m in electrical school and we’re learning about series circuits and I was just randomly thinking about voltage drop across devices and was wondering how does electricity “know” to not have the voltage drop to zero at the first device in a series circuit and to drop the voltage according to its individual value of resistance compared to the total resistance of the circuit and divide it accordingly across every device on the circuit until it reaches zero.
In: Physics
It doesn’t know. In fact, *initially*, it doesn’t nicely divide the voltage drops across every element at all, there are transient effects. They’re just so fast in most circuits that you don’t notice them and we achieve the steady state values “instantly”.
The reason it *ends up* that way is that’s the only solution where everything is stable in time. If the values were anything else there’d be an imbalance between voltage, current, and resistance somewhere in the circuit and (at least) one of them would be changing.
At the initial instant you connect the circuit the current is zero. The voltage on one side of the first device is the supply voltage, the voltage everywhere else is 0. The first device sees the *full* voltage…current spikes…this is “inrush current”. As soon as it starts to flow you start getting a voltage drop across that device. Now the volage on the other side is something less than supply and the next device down the line sees that lower voltage, which starts pushing current through that device, and so on. The voltages and currents keep bounding around in the circuit until everything stabilizes and *that* the value that you calculate using the basic resistance rules. This happens *very* quickly in normal circuits. Once you get to oscillating circuits and inductors this should make way more sense.
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