# Alternating Current question

1. Feb 5, 2012

### SirBerr

My professor crammed an alternating current (AC) into one lesson. I have an OK understanding of AC but my question is as follows. Let's assume that our voltage goes from 60V to -60V, at some point the potential difference is 0 and I would think the current itself would also be 0. Does that mean that an object that was being powered would actually turn off instantaneously at this exact time? I don't think that an object would but am having a difficult time figuring out as to why they don't.

Thanks

2. Feb 5, 2012

### Studiot

Yes indeed apparatus does turn on and off as you suggest.

This is why the AC mains is 50 -60 Hz - it is the lowest frequency that old fashioned light bulbs will not appear to flicker. You can definitely see this effect with say 25 Hz.

The situation is complicated by two things.

Firstly equipment such as electric motors have inertia in the rotating wheels so carry on past the zero point.

Secondly the current zero and voltage sero only occur simultaneously for circuits containing pure resistance. Reactive circuits have a phase difference between current and voltage.

3. Feb 5, 2012

### technician

You may see fluorescent lights flickering because they can respond to this frequency but filament bulbs have too much ' thermal inertia' to show any dimming.
Rotating machinery running on mains frequency may show stroboscopic effects if illuminated only by fluorescent lighting
Edit..
Agree with studiot...just seen it

Last edited: Feb 5, 2012
4. Feb 5, 2012