How can current flow in A/C circuits?

1. Oct 5, 2008

Farlander

How can current flow in A/C circuits!?

Hello everyone!

In alternating current circuits, such as the North American main power grid, voltage swings from 120V to -120V at a rate of 50-60 cycles per second, right? If that's true, than how can current ever reach the load?? It seems like the electromotive force would prevent any amps from actually moving....

2. Oct 5, 2008

Staff: Mentor

Re: How can current flow in A/C circuits!?

The current (everywhere in the circuit) oscillates back and forth through the load.

3. Oct 5, 2008

subtech

Re: How can current flow in A/C circuits!?

Assuming an 80% velocity factor and a system frequency of 60 Hz, the current leaving
the generator will travel well over 1000 miles before the polarity of the EMF reverses.
I think those electrons can get to any load and back to the generator quite handily.

4. Oct 5, 2008

Staff: Mentor

Re: How can current flow in A/C circuits!?

In fact, even if the electrons don't move quite that fast or the distance is much further, you'll just have several waves traveling down the wire at the same time.

5. Oct 5, 2008

Redbelly98

Staff Emeritus
Re: How can current flow in A/C circuits!?

I'm not fond of the water flow analogy, but it works to answer this question.

Imagine a garden hose full of water, but the faucet is off. Then you turn the faucet on. Almost immediately, water starts coming out the end of the hose. Even though individual water molecules may take 10 seconds or so to travel the length of the hose, all water molecules begin moving as soon as the faucet is turned on, and the "current" is set up practically instantaneously.

Turning current on or off, or reversing current as part of the line cycle, works pretty much the same way.