I have been looking in to alternating current and I am confused. If the voltage reverses doesn't the flow of electrons also reverse? I am aware of another fair answer on this site here. That answer, however, confused me just a bit. I gathered that the electrons do not per se "flow." Is this true? How is the electrical current moving?
Answer
There is a commonly used analogy for electric circuits called the hydraulic analogy. This imagines the electrons as water and the wires as pipes. The voltage is equivalent to the water pressure and the current is equivalent to the water flow rate.
Start with a DC current and imagine the water is doing work by flowing through a water wheel:
This is all very straightforward: the water/current flows steadily through pipe/wire and turns the waterwheel/electric motor, which can then do work.
But now suppose we pump the water from left to right, then reverse the pump and pump the water from right to left.
This is exactly what an alternating voltage does. The water just moves to and fro within the pipe so there is no net flow. However the water can still move the waterwheel, but it moves it to and fro rather than at a steady rotation speed. We can still get the waterwheel to do work - if you're using it to grind corn it doesn't matter whether the wheel is rotating steadily or moving to and fro. The corn still gets ground.
Likewise, with an alternating voltage the electrons oscillate to and fro in the wire so there is no net flow of electrons. But the electrons can still do work e.g. heat a light bulb or run a (suitably wired) electric motor.
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