Why don't objects turn off when an AC circuit reaches 0V?

Click For Summary

Discussion Overview

The discussion revolves around the behavior of objects powered by alternating current (AC) when the voltage reaches zero. Participants explore the implications of voltage and current reaching zero in AC circuits, particularly in relation to the operation of electrical devices and the perception of flickering in lights.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether objects powered by AC turn off instantaneously when the voltage is zero, expressing uncertainty about the behavior of current at that moment.
  • Another participant asserts that apparatus does indeed turn on and off as suggested, referencing the frequency of AC mains as a factor in preventing flickering in traditional light bulbs.
  • It is noted that electric motors have inertia, allowing them to continue operating past the zero voltage point, complicating the situation.
  • Participants mention that current and voltage reach zero simultaneously only in pure resistive circuits, while reactive circuits exhibit a phase difference between current and voltage.
  • Fluorescent lights may flicker at lower frequencies, while filament bulbs do not show dimming due to thermal inertia.

Areas of Agreement / Disagreement

Participants express differing views on whether objects turn off instantaneously at zero voltage, with some agreeing that they do not, while others provide explanations that suggest a more complex interaction involving inertia and phase differences. The discussion remains unresolved regarding the precise nature of this behavior.

Contextual Notes

The discussion highlights the limitations of understanding related to the behavior of AC circuits, particularly regarding the assumptions about simultaneous zero voltage and current, as well as the effects of different types of electrical devices.

SirBerr
Messages
9
Reaction score
0
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
 
Physics news on Phys.org
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

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.
 
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:
Studiot said:
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.

I thought I just had bad eye sight.

Thanks a lot!
 

Similar threads

  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 17 ·
Replies
17
Views
3K
  • · Replies 13 ·
Replies
13
Views
3K
  • · Replies 30 ·
2
Replies
30
Views
3K
Replies
152
Views
8K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
Replies
5
Views
2K