Current flow in AC circuits

Physics Asked by Simon Baughurst on December 23, 2020

First off I apologise if these questions have been asked numerous times before.

I’m having trouble visualising the flow off electrons in an AC circuit, particularly with a grounded neutral at earth potential.

My understanding is that during the positive cycle of AC electrons flow through the neutral and load towards the higher potential, the area with an abundance of positively charged protons? Now if that’s correct are the electrons being pushed with volts and if so how when neutral carries no volts.

I’m hoping someone can see the fundamental information I’m missing and can clear my confusion.

2 Answers

What drives the current through the load is a difference in potentials (potential difference or voltage) between one end of the load and the other. Compare this with the flow of liquid through a pipe being due to a pressure difference between the ends of the pipe.

On both halves of the cycle there is a pd across the load. On one half cycle the neutral is at a lower potential than the live; on the other half the neutral is at a higher potential than the live. So, either way, there will be a current.

The only reason that the neutral is called 'neutral' is that it is connected to the ground, or at least close to ground potential, meaning that if you are standing on the ground with poorly insulating shoes and touch the neutral wire, it should not be life-threatening, but NEVER DO IT - there can be mistakes.

Answered by Philip Wood on December 23, 2020

If you have a tank of water sitting on the ground, does water flow into it or out of it?

It depends on what the alternatives are. If you have water at a higher gravitational potential (like up on a table), then water will flow from the one on the table to the one on the ground.

If you have a tank down in the basement, then water will flow from the tank on the ground to the one in the basement.

The same is true for the wires in your circuit. The fact that one of the wires has a voltage that is called 0 is just a convenience. All that matters for the circuit is what the difference is between the wires.

Electrons will flow from the lower potential to the higher potential. Sometimes the "line" or "live" wire is above the neutral/reference potential and sometimes it is below it. So charge will tend to flow in opposite directions during the two portions of the cycle.

Answered by BowlOfRed on December 23, 2020

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