Questions about Resistance, Capacitors in Circuits

[mneox]

Homework Statement

hi guys, i just have some theory and general questions about circuits. hope you can bear with me and be able to help me out cause I'm trying to grasp the ideas. thanks!

1) i have a RC circuit that has a switch. if the switch was close for a long time and then opened again, what does this mean?

i know that when the switch first closes, the current flows through the capacitor, and eventually the capacitor does not for current to flow through anymore. (the capacitor charges with the voltage increase)

so what does opening the switch after it has been closed for a long time do? what happens?

2) when exactly does a capacitor discharge? is it when it at max charge?

3) say i have current flowing through the circuit, and it enters a junction that splits into two branches. one branch has a 3 ohm resistor, the other is just a normal wire with no resistance.

i remember hearing about how current travels in the path of least resistance. so does this mean that the current will only travel through the 0-resistance wire? or no? I'm confused about that.

Homework Equations

Not sure if i really need any for my questions but uh
V=IR
P=IV
V=Q/C

The Attempt at a Solution

Hope someone can help me answer these questions, I'm just trying to make sense of it all! :)

Thank you for your help and time guys

 

[gneill]

Homework Statement

hi guys, i just have some theory and general questions about circuits. hope you can bear with me and be able to help me out cause I'm trying to grasp the ideas. thanks!

1) i have a RC circuit that has a switch. if the switch was close for a long time and then opened again, what does this mean?

i know that when the switch first closes, the current flows through the capacitor, and eventually the capacitor does not for current to flow through anymore. (the capacitor charges with the voltage increase)

so what does opening the switch after it has been closed for a long time do? what happens?

Nothing happens if there is no longer a complete circuit (loop) for current to flow. The charge on the capacitor just sits there.

2) when exactly does a capacitor discharge? is it when it at max charge?

It discharges when it has a closed path between its terminals that will allow current to flow between them in such a way as to remove existing charge from the capacitor. Note that the path may or may not include voltage or current sources that can drive said current or make the final state something other than zero charge on the capacitor.

3) say i have current flowing through the circuit, and it enters a junction that splits into two branches. one branch has a 3 ohm resistor, the other is just a normal wire with no resistance.

i remember hearing about how current travels in the path of least resistance. so does this mean that the current will only travel through the 0-resistance wire? or no? I'm confused about that.

The phrase "current takes the path of least resistance" is misleading, because it implies that all the current always takes the path that has the least resistance. So if there were two paths, one with 10 Ohms and one with 9.9 Ohms, it would imply that all the current passes through the 9.9 Ohm path and none through the 10 Ohm path. This is not the case.

In general, current takes ALL paths available but divides according to the conductances of the paths. That is, paths with greater conductance will take more of the current. Conductance is the inverse of resistance: G = 1/R. In the limit where one of the paths approaches infinite conductance (zero resistance), all of the current will take that path.