# AC current

1. Apr 27, 2013

### M.Kalai vanan

what does the positive and negative half cycles in an ac represent?

2. Apr 27, 2013

### phinds

The direction of the current. That's why it's called ALTERNATING current.

3. Apr 27, 2013

### skeptic2

What does the C in AC stand for?

4. Apr 27, 2013

### jim hardy

I gather you're referring to a waveform?
It's a graph of volts versus time.
Traditionally horizontal axis is time; vertical is voltage with positive up and negative down.

5. Apr 28, 2013

Personally I never liked the "C" - because power requires voltage AND current. In AC BOTH the voltage and current change polarity - so (typically) the power is always flowing in one direction.

6. Sep 19, 2016

### leonalee

Positive and negative cycles represent the direction of the alternating current.AC reverses its direction many times in a second.Number of times it changes its direction in a second is measured as frequency.Go through the Alternating current for more information..

7. Sep 19, 2016

### Staff: Mentor

Except for the special case of the load being purely resistive, the power in AC does alternate with each positive pulse followed by a smaller negative pulse to deliver an average power that is positive.

8. Sep 19, 2016

### anorlunda

Sorry, but no. The positive and negative half cycles are the same size and there is no pulsing. When V and I are in-phase, V*I is positive when both V and I are positive, and V*I is positive when V and I are both negative. Look at the drawings in the Insight article.
https://www.physicsforums.com/insights/ac-power-analysis-part-1-basics/

9. Sep 19, 2016

### Staff: Mentor

Maybe you didn't understand what I wrote?

That's a useful article, including this figure which neatly illustrates the general case I describe:

Last edited: Sep 19, 2016