# AC direction change - how does electricity flow?

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1. May 24, 2015

### matilda

If drift velocity of electrons changes in AC, how does electricity flow through a circuit to then lose potential energy to the devices in the circuit?

Also considering the change in direction, does that mean that the live wire and neutral wire also switch roles in AC mains? I am very confused about this.

2. May 24, 2015

### theodoros.mihos

A wire is something like a line with charge carriers and all rest world with no carriers. This is like an 1D world for electric field, even wire may have complex shape. The energy that these field carriers transfer to a positive charge q on the wire:
$$dW = dF\,dx = -E\,q\,dx$$
that mean the electric field give energy to q for all period, because E and dx change direction together.
Confusion comes for using DC terms to solve AC circuits but devices work differntial on AC or DC voltage. i.e. a capacitor has infinity resistance on DC and 1/ωC on AC, and this "resistance" differs to Ohmic resistance nature.

3. May 24, 2015

### anorlunda

You will find elecricity much easier to understand if you forget about drift velocity and analogies to massive particle kinetic and potential energies.

Imagine a person holding the ends of a rope wrapped around a remote pulley. He moves the rope back and forth, causing the axle of the pulley to heat because of friction. The person is transmitting energy to a remote location in a manner analogous to AC electricity. But the molecules in the rope are not drifting at all, nor are their kinetic or potential energies important.