# Thread: How the circuit "knows" to change the current

1. Let's say there is DC circuit with an EMF of 20V and a resistor of 2 Ohms. The current then is 10 Amps.

Now we add another resisotr (in series) of 2 Ohms and we get a current of 5 Amps.

At the moment the current starts - hoes does it "know" that amother resistor was added and that it should "reduce itself" to 5 Amps?

2. Originally Posted by rotem300100
Let's say there is DC circuit with an EMF of 20V and a resistor of 2 Ohms. The current then is 10 Amps.

Now we add another resisotr (in series) of 2 Ohms and we get a current of 5 Amps.

At the moment the current starts - hoes does it "know" that amother resistor was added and that it should "reduce itself" to 5 Amps?
In exactly the same way that the circuit “knew” to make the current 10 amps with the original 2 ohm resistor.

You have to recognize that these are steady-state values. The current does not jump up instantaneously. To provide a solution that is valid before the steady-state condition is reached requires an agreement on the model you wish to use. For example, pure, ideal resistors that act as such over all frequencies do not exist, so you have to decide on the abstraction level you accept, and then analysis can proceed from there.

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