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Where do electrons come from in a circuit?

by FeDeX_LaTeX
Tags: circuit, electrons
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FeDeX_LaTeX
#1
Mar15-10, 02:30 PM
P: 427
Hello;

When we put a battery in a circuit and connect up all the wires, a current flows. This is a flow of electrons. But where do these electrons come from? Were they being stored inside the battery?

Thanks.
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f95toli
#2
Mar15-10, 02:34 PM
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No, not as such. There are -by defintion- always plenty of free electrons in a conductor.
Also, note that an electrical circuit is not "using" electrons; it is just pushing them around meaning there is no way you can "run out" of electrons as long as there is a potential difference that can drive a current.
Cvan
#3
Mar15-10, 02:36 PM
P: 87
The electrons are just there. Think of the circuit as a system of pipes. The pipes are completely full with water, but without the battery connected the water doesn't move. Now, what happens if you suck on one side of the pipe (cause a pressure difference between the 'beginning' and 'end')? Water flows through the circuit. Same idea with the electrons in a circuit. Battery cell provides the potential difference (voltage) to cause electrons inside the wires to move through the circuit. Note: The electrons don't actually move that fast! They move around 10^-4 or 10^-5 m/s (I forget which order), but regardless, it's the same with water though. The important thing is that when you push on one side of the electrons in the wire, all of the electrons get pushed together since they're all squished together in the first place, and electrons don't like to get close to another more than they have to (same with nearly incompressible water!). Think: I suck on one side of the pipe in the water circuit (but not much) causing a small potential difference. The other side will almost immediately move, but the water in general wasn't moving that fast.

Hope this helps.

FeDeX_LaTeX
#4
Mar17-10, 02:38 AM
P: 427
Where do electrons come from in a circuit?

Okay, that makes sense.

So if there were no electrons in a circuit, there would be no current then?
rcgldr
#5
Mar17-10, 02:52 AM
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The negative terminal of a battery is connnected to a mass of negatively charged ion's with extra electron(s) in each molecule, while the postive terminal is connected to a mass of positively charged ions with missing electron(s) in each molecule. When current is flowing, electrons flow out from the negatively charged ions, and other electrons flow into the positively charged ions.

The speed of the electrons is quite fast, but most of this motion is random, with only a small component of net flow in the direction of "electron flow".
FeDeX_LaTeX
#6
Mar17-10, 03:01 AM
P: 427
So if the electron flow comes from the masses of ions within the circuit, does this mean that the ions move too? Or do the electrons separate from the ions because they are moving?
Lok
#7
Mar17-10, 03:12 AM
P: 463
Quote Quote by FeDeX_LaTeX View Post
So if the electron flow comes from the masses of ions within the circuit, does this mean that the ions move too? Or do the electrons separate from the ions because they are moving?
Depends on the material used. In metals there is practically no + ionic movement in normal conditions, but in ionic solutions ions are the only charge carriers (both + and -), no free moving electrons though as they are bound to their respective negative ion.
f95toli
#8
Mar17-10, 05:49 AM
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Quote Quote by FeDeX_LaTeX View Post
So if there were no electrons in a circuit, there would be no current then?
Exactly, a material with no free electrons is known as an insulator.


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