Some theory type questions.....

[Dont_Taz_Me_Bro]

I've been trying to wrap my head around what exactly is happening on the electron level when a voltage source is applied to a circuit. I'm not really interested in the math behind it....just a general description of what is happening.

I've heard of the analogy that voltage is equal to water pressure and current is equal to the volumetric flow rate.

I'm under the impression that individual electrons aren't necessarily "flowing" around a circuit, but instead are bumping into each other and transferring energy....is this correct? So before a voltage is applied are electrons just sitting around the wires of the circuit....or do they only disperse throughout a circuit once you turn the battery on?

So resistors restrict or limit the current flow...right?

How exactly do they do this? What is physically happening between the electrons and the resistor material?

I'm having trouble seeing how the electrons move around and interact in the circuit within my mind......so if anybody could just provide an example of a simple circuit and how exactly the electrons are moving and transferring energy....I'd appreciate it.

Also, according to conservation of energy....all of the voltage provided by the source must be used in the circuit...right? So if an LED or some other device only uses a fraction of the total voltage you need to use resistors to make sure the device isn't damaged?

What I've heard is that it doesn't matter if you put the resistor before or after the device.....but this confuses me since I'm under the impression that the electrons (current) travels from the negative terminal of the battery around the circuit and back to the positive. If this is the case wouldn't you want to put the resistor between the device and the negative terminal of the battery?

I imagine these questions are as simple as it gets, but I'm still hoping somebody will take the time to straighten me out.

Thanks

[waltr]

I think I can help a little.

The water analogy can work up to a point, its ok for simple DC circuits.
Think of voltage as potential, technically voltage is called the electrical potential (symbol E as in E = IR, Ohms law). Now in mechanics and the water analogy, potential is the difference in a height, so a higher voltage is partly equivalent to a greater height difference between the positive and negative terminal (battery). So think of the battery having a pool of water at some height above another pool of water.
A connection across the battery is equivalent to a opening in the side of the top pool of water that allows the water to drain from the top pool to the bottom pool. Once all the water drains out the battery is discharged or dead.
A heavy piece of wire (low resistance) is like just totally opening the side of the top pool of water. Lots of water flows down in a short time. The amount of water (volume) that flows in a fixed period of time is equivalent to current flow from a battery (and through a circuit).
A resistor in the water analogy restricts the flow (current or water). This is equivalent to a pipe with a smaller opening in the top pool of water connecting to the bottom pool. The height drop is the same but less water flows out of the top pool in a fixed period of time.

Hope you are following.
So, the voltage or potential is across a circuit and the current is the number (volume) of electrons per unit time. With the water analogy one could connect the upper pool to the lower pool by a tube or pipe. The diameter of the pipe is inversely equivalent to the resistance of a resistor (small pipe gives a  high resistance to the flow). Even if you have several pipes connected together (series resistors) the flow at any point in the pipe is the same.

As to what each electron is doing and how circuit components effect them is a bit beyond my ability to easily explain. Maybe some one else can.

Did this help?

[Dont_Taz_Me_Bro]

Thx Waltr for your reply....

Let me see if I understand what you are saying:

So essentially a resistor is just choking off the amount of energy that can pass through……does this equate to reducing the number of electrons that pass through a given cross section of wire at a given time?

Also, when I think of a fluid getting choked off....I also realize that it speeds up. So despite the fact the volume has diminished the speed should have increased. How would this affect the current?

Also, by reducing this amount of energy passing through the resistor, do the electrons essentially "back up" and create more pressure (voltage) before the resistor?

[waltr]

So essentially a resistor is just choking off the amount of energy that can pass through……does this equate to reducing the number of electrons that pass through a given cross section of wire at a given time?

In essence yes.

Also, when I think of a fluid getting choked off....I also realize that it speeds up. So despite the fact the volume has diminished the speed should have increased. How would this affect the current?

Also, by reducing this amount of energy passing through the resistor, do the electrons essentially "back up" and create more pressure (voltage) before the resistor?

These are cases in which the water to electron analogy breaks down and can not be used.

Electron flow does NOT translate to an analogy in fluid dynamics. Check Wiki for a definition of current flow:
http://en.wikipedia.org/wiki/Ampere
And the Wiki for voltage and the water analogy written better than I have explained it.
http://en.wikipedia.org/wiki/Voltage

[Dont_Taz_Me_Bro]

Appreciate your response...thx again