# What forces are acting on electron in a circuit? Do electrons act on each other in a current?

What forces are acting on electron in a circuit?

What is the source of such kind of forces?

Do electrons act on each other in electric current?

If i have an ordinary electric circuit with only one resistor, then if i raise resistance, the electric current goes down. As I understand it happens because the vector $$\vec E$$ of elecric field inside the conductor goes down. The main question is how electric field (vector $$\vec E$$) "feels" that i raised resistance? Well if I have a water flow in a tube i can imagine it. Assume some obstacle suddenly appears in a tube, then it stops the nearest moving molecules of water. This molecules of water stop molecules behind them, which then stops molecules behind them ...etc. And then all molecules are stopped. That's because molecules act on each other. It's like standing in a queue or walking in a crowd. If some man in front of me stops, then I will stop and the man behind of me will stop too. But what about electric current? Is it the same process? Do electrons act each other like molecules of water or like people in a crowd? If it's true that means electric field caused by electrons themself? I'm not only interested about how electric field distributed inside a conductor, I'm interested about the source of that field too.

• – anna v May 28 at 14:48

If i have an ordinary electric circuit with only one resistor, then if i raise resistance, the electric current goes down. As I understand it happens because the vector $$\vec{E}$$ of elecric field inside the conductor goes down.

It depends if you changed the resistance by changing the effective length of the resistor or by changing the cross-sectional area of the resistor or by changing the composition of the resistor.

If you just changed the length of the resistor, then yes, you reduced $$|\vec{E}|$$ in the resistor.

But if you changed the cross-sectional area of the resistor or the composition, without changing the length, then $$|\vec{E}|$$ hasn't changed.

Do electrons act each other like molecules of water or like people in a crowd?

More or less, yes. When you apply a negative voltage to one end of a wire, you're essentially pushing some electrons onto that end of the wire. These push the electrons that are already in the wire, which push the electrons that are a bit further along, and so on, until some electrons are pushed out the other end of the wire onto the positive terminal of the source you're using to apply the voltage.

I'm interested about the source of that field too.

The source is whatever device you used to apply the voltage to the ends of the wire. It could be a battery, or a turbine-driven generator, or a power supply circuit, or a number of other things.

If it's true that means electric field caused by electrons themself?

Yes, of course. Electrons are charged particles, therefore they produce electric field.

• Well, I mean vector E in the wire, not in resistor. Even if you're talking about the resistor and change cross-sectional area or composition without changing the length, and as you say vector E wouldn't change, then according to differential form of Ohm's law J = σE the current densitity wouldn't change and that means the electric current wouldn't change which is a contradiction of Ohm's law. By the way when I say the source of forces I don't mean devices, I mean the source in terms of particles. – Eugene May 30 at 5:24
• @Eugene, the field in the wire is usually negligibly small compared to the field in the resistor or in the space around the wire. It "doesn't change" in the sense that approximately zero isn't different from some other approximate zero. But of course if the current in the wire changes, then the E field strength must have also changed proportionally. – The Photon May 30 at 5:31
• But what about vector E in the resistor. You say it wouldn't change if the length doesn't change, that means that current density would change. – Eugene May 30 at 5:38