Help with Circuits

[constantreverie]

Hello, I was hoping someone could clear things up for me.
I am studying circuits, and I get the basics, but I get confused because it seems like sometimes the resistance can change, and sometimes its constant. Same with voltage, for example if you have resistors in parallel then the voltage seems to get split up between the different paths.

When are V,I,R, and C able to change and when are they constant?
Thanks in advanced.

Oh another thing that confused me about it, there was a problem where you had resistors in parallel, there were 3 of them. and the middle one had a switch. The question asked what would change if the switch closed, and the answer was that the current would stay the same. But I thought that since you added another resistor in parallel, the resistance would change, and the voltage would change. However, it was saying that the voltage drop would be the same, as if the voltage goes through the middle one even though the switch was open. Sorry if that doesnt make sense.

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[NextStepTutor_1]

Try to think about circuits in terms of current. It's easier.

The current in the total circuit (an ideal circuit) is constant. Resistors in parallel have differing currents because the current will try to take the path of least resistance at the point at which the current could go to one or the other resistor. However, the voltage is the same across these resistors, but not the same as the voltage of the battery.

For resistors in series, the current has no option but to continue through them equally - thus the current through these resistors is the same. This means that what determines if their voltages across them are different or the same is if their resistances are different or the same, respectively.