Voltage and Current conceptual.

[MedPR]

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I'm trying to get a conceptual understanding of why resistors in series share the same current but have different voltage drops, and why resistors in parallel share the same voltage, yet have different currents.

I understand that the current before and after a junction must be equal. So it makes sense to me why the resistors in series have the same current flow through them; there is no junction. It also makes sense why parallel resistors have different current, because there is at least 1 junction where the current must "split". In other words, I1+I2=Itotal. Good.

What I don't understand is why voltage does not follow the same rule. Why can voltage before the junction be the same at all parts of the junction?

 

[milski]

Voltage is a difference in potential. As the charges move through some resistance, they lose some of their potential. The more resistance there is, the more the potential will drop. In the case with parallel resistors, the charges in each 'branch' are independent from the charges in the other branches, so how much potential they are going to lose depends only on what they encounter in that branch.

 

[MedPR]

Voltage is a difference in potential. As the charges move through some resistance, they lose some of their potential. The more resistance there is, the more the potential will drop. In the case with parallel resistors, the charges in each 'branch' are independent from the charges in the other branches, so how much potential they are going to lose depends only on what they encounter in that branch.

So if you have no resistors or capacitors in a circuit, what happens? No potential is lost.. what does that lead to?

 

[MT Headed]

So if you have no resistors or capacitors in a circuit, what happens? No potential is lost.. what does that lead to?

If there still a battery in the circuit, then you have to take into account the internal resistance of the battery and/or the wire itself. A battery is really a battery plus a teeny resistor that is often discounted because it is so small. A wire does have a teeny amount of resistance too, usually ignored.

In real life, the voltage drop will be whatever the voltage of the battery is, the resistance will be microscopic, and the current therefore will be enormous. Therefore the P=I*V will be astronomical, and the entire system will heat up and probably catch on fire.

It's called a "short circuit" and there are circuit breakers in houses to prevent this and keep houses from catching on fire.

 

[MedPR]

If there still a battery in the circuit, then you have to take into account the internal resistance of the battery and/or the wire itself. A battery is really a battery plus a teeny resistor that is often discounted because it is so small. A wire does have a teeny amount of resistance too, usually ignored.

In real life, the voltage drop will be whatever the voltage of the battery is, the resistance will be microscopic, and the current therefore will be enormous. Therefore the P=I*V will be astronomical, and the entire system will heat up and probably catch on fire.

It's called a "short circuit" and there are circuit breakers in houses to prevent this and keep houses from catching on fire.

I see, thank you.

I'm still not exactly understanding how the potential doesn't need split up along different paths the same way that current does. In the analogies with water flow, current is the volume flow rate. What is the voltage? How high the waterfall is above the ground? If yes, that doesn't help me understand (sorry!).

 

[MT Headed]

I see, thank you.

I'm still not exactly understanding how the potential doesn't need split up along different paths the same way that current does. In the analogies with water flow, current is the volume flow rate. What is the voltage? How high the waterfall is above the ground? If yes, that doesn't help me understand (sorry!).

It is analogous to the height of the water-pipe, but I can see how the analogy is failing you.

The way I like to think of it is that you can point to a point on a wire (like the part that touches the ground of the battery) and declare that it has a voltage, like 0V. Now, that 0V is going to be the voltage at every point along the wire. Once you pass through an object, like a 6V battery, then the voltage on the wire on the other side is going to be +6V. Everywhere along that section of wire. Even if it splits into multiple branches, each of those branches will also be at +6V.

More practice will help, one day it will all click. Promise!

 

[MedPR]

It is analogous to the height of the water-pipe, but I can see how the analogy is failing you.

The way I like to think of it is that you can point to a point on a wire (like the part that touches the ground of the battery) and declare that it has a voltage, like 0V. Now, that 0V is going to be the voltage at every point along the wire. Once you pass through an object, like a 6V battery, then the voltage on the wire on the other side is going to be +6V. Everywhere along that section of wire. Even if it splits into multiple branches, each of those branches will also be at +6V.

More practice will help, one day it will all click. Promise!

Yea I can do the problems now that I've memorized the concept, but I don't know if that means I'm understanding it or not. I've basically memorized that series = same current and different voltage drop. Opposite for parallel.

I'm still a little confused about the reasoning behind a lot of the calculations. I can do them, but they don't make sense. I'll post an example a little later when I get a break at work.