# Formation of surface charge densities on wires in simple DC circuits

• Strafespar
In summary, the surface charge densities shown in the pictures are stable because there is always some charge to produce the electric field.
Strafespar
Currently using resources like:
http://www.matterandinteractions.org/Content/Articles/circuit.pdf
http://www.phy-astr.gsu.edu/cymbalyuk/Lecture16.pdf

I don't seem to understand why the surface charge densities shown in the pictures are stable. I understand that the densities shown create constant electric fields which drive the current, but not why the surface charges themselves are not subjected to movement.

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They may move slowly along the surface. The only requirement is that there is always some charge to produce the electric field in the wire, and to do that, they do not need to be static.

1 person
Jano L. said:
They may move slowly along the surface. The only requirement is that there is always some charge to produce the electric field in the wire, and to do that, they do not need to be static.

Oh ok, I think I understand. So is the charge distribution at any particular time representative of the electric field at those positions? I.e. in areas of high charge distribution is there a lesser electric field and areas of low charge distribution a greater electric field (electric field operating on surface charges NOT the inside ones in the wire). What I am getting at is: that there is less likely to be more charges at areas of high electric field, etc.

I.e. in areas of high charge distribution is there a lesser electric field and areas of low charge distribution a greater electric field

I think it is the opposite; in order to produce higher electric field in the metal point P, there has to be more charges close to this point P on the surface.

The Sherwood paper is interesting because it seems to have been produced in response to a very 'combative' attitude from present day students, to matters that confuse them. He has clearly thought about many of the niggles that students have when approaching the topic of Electricity and has addressed many of the problems very positively and thoughtfully. (The word 'indulgent' springs to mind.)

The fact is that you need to approach every problem and situation at an appropriate level. (There are 'shells' of understanding in all Science). Circuit problems are nearly always best dealt with by assuming there is no resistance in wires, that the PD is zero and the route taken by the wire is irrelevant. A connecting wire with no (or very low) resistance can be treated in much the same way as a roller coaster track (in a vacuum etc.). In both cases, the energy loss is zero, whatever the path of the wire or the peaks and dips in the track. Ideal roller coaster cars would arrive at the bottom at the same speed, whatever route they took.
Imo, there is little point in worrying about the local charge distribution (except in a very arm-waving way) unless you are going the whole hog and also consider the Capacitance and Inductances involved.

## 1. How do surface charge densities form on wires in simple DC circuits?

Surface charge densities form on wires in simple DC circuits due to the transfer of electrons from the negative terminal of the power source to the wire. This creates an excess of negative charge on the surface of the wire, resulting in a surface charge density.

## 2. What factors influence the magnitude of surface charge densities on wires?

The magnitude of surface charge densities on wires is influenced by the voltage of the power source, the resistance of the wire, and the length and cross-sectional area of the wire. Higher voltages, lower resistance, and longer or thicker wires tend to result in higher surface charge densities.

## 3. Can surface charge densities on wires be positive?

Yes, surface charge densities on wires can be positive if the wire is connected to the positive terminal of the power source. In this case, there will be an excess of positive charge on the surface of the wire.

## 4. How do surface charge densities affect the flow of current in a circuit?

Surface charge densities do not directly affect the flow of current in a circuit. However, they can indirectly affect the resistance of the wire, which in turn affects the flow of current. Higher surface charge densities can lead to an increase in resistance, making it more difficult for current to flow through the wire.

## 5. Can surface charge densities on wires be controlled in a DC circuit?

Surface charge densities on wires can be controlled to some extent by adjusting the voltage, resistance, and length or thickness of the wire. However, they are also influenced by external factors such as humidity and temperature. In some cases, additional measures such as using insulating materials or grounding the wire may be necessary to control surface charge densities.

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