Is Pulsing Current the Same as Alternating Current?

Click For Summary

Discussion Overview

The discussion revolves around the definitions and characteristics of pulsing current and alternating current (AC). Participants explore whether a current must change direction to be classified as AC and consider scenarios where the current's magnitude varies while its direction remains constant.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants question if a current needs to change direction to be considered AC, proposing that a varying magnitude without direction change could still be significant.
  • One participant asserts that regular AC current reverses direction due to the voltage oscillating between positive and negative, suggesting that a purely unidirectional current varying in magnitude would not qualify as AC.
  • Another participant agrees that for a current to be classified as AC, it must periodically change direction, typically alternating around a mean amplitude of 0A, but notes that a DC offset can shift this mean amplitude.
  • A participant raises a question about the application of AC circuit laws to a sinusoidally varying DC current, specifically regarding the behavior of current in relation to voltage across a capacitor.
  • One participant explains the principle of linear superposition in circuits, indicating that signals can be decomposed and analyzed independently, maintaining the leading or lagging properties due to circuit elements.
  • Another participant introduces the term "pulsating DC" to describe a current that varies in magnitude without changing direction.
  • One participant concludes that pulsing current is distinct from AC, emphasizing that AC, by definition, alternates.

Areas of Agreement / Disagreement

Participants express differing views on whether pulsing current can be classified as AC, with no consensus reached on the definitions and implications of these terms.

Contextual Notes

Participants discuss various scenarios involving DC offsets and the implications for circuit behavior, but the discussion does not resolve the definitions or applications of pulsing current versus AC.

Apteronotus
Messages
201
Reaction score
0
Does a current need to change direction in order to be considered as an AC?

What if the direction remains the same, but the amount of current which flows varies with time, as in a sine wave?

Thanks
 
Physics news on Phys.org
Regular AC current reverses direction because the voltage goes form positive to negative in a sign wave
You could build a system where the voltage varied from 0 to a positive voltage and back again - so current was always in one direction.
But this couldn't be a sin wave, it would be mod(sin) or sin^2

Or you could add a DC offset to an AC signal so it was still a sin wave but went from 2*V to 0
 
Last edited:
Apteronotus said:
Does a current need to change direction in order to be considered as an AC?

What if the direction remains the same, but the amount of current which flows varies with time, as in a sine wave?

Yes, for a current to qualify as alternating (i.e. AC), it has to periodically change direction. In other words, the current is sometimes positive and sometimes negative relative to a defined positive direction at a point in the circuit.

Normally the current alternates around a mean amplitude of 0A. However, you can move this mean amplitude up and down as you like by adding a DC offset. E.g. if you have a 2Apk-pk AC signal alternating around 0A and add a 1A DC offset, the current will remain in one direction, and you have a sinusoidally varying DC current.
 
So would the laws of AC circuits apply in such a case.

For example if in fact we do move the mean amplitude up so that we have a sinusoidally varying DC current and our circuit comprises of a simple capacitor, would the current in the capacitor lead the voltage?
 
Circuits follow linear superposition. So whatever components that you can break up the excitations into, you can solve for them individually and then add up the results to get the full answer (This does not always include nonlinear circuit elements like diodes and transistors since, for example, the individual voltage components may not be large enough for turn on voltages but together they could be. However, if we know what state they are operating in then we can properly apply superposition.). So if we can decompose our voltage signal into an AC signal with a DC offset, we could solve for the two signals independently and add them together. So there will still be a lagging/leading property to the signals due to capacitive and inductive elements.
 
Apteronotus said:
What if the direction remains the same, but the amount of current which flows varies with time, as in a sine wave?

In case anyone's interested -- that's called pulsating DC.
 
That is fantastic. Thank you all very much.
 
pulsing current is just pulsing current. AC by definition means it alternates.
 

Similar threads

High School Coil that conducts direct current
  • · Replies 8 ·
Replies
8
Views
1K
High School A question about induced current in LC circuits
  • · Replies 4 ·
Replies
4
Views
2K
High School The historical war of currents in Mains Power Distribution: AC vs DC
  • · Replies 7 ·
Replies
7
Views
2K
High School Why is there induced current in a DC motor?
  • · Replies 2 ·
Replies
2
Views
1K
Undergrad Current's Effect on Electrical Arcs
  • · Replies 9 ·
Replies
9
Views
4K
Undergrad Which law defines the AC inducing voltage in the inductor?
  • · Replies 25 ·
Replies
25
Views
3K
Graduate Hall Effect in an alternating current circuit
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad DC current flows in a wire when two loops are brought close by?
  • · Replies 14 ·
Replies
14
Views
2K
Undergrad Can current flow in an open circuit?
  • · Replies 4 ·
Replies
4
Views
3K
High School Single phase induction motor Torque under increased frequency and Same Current
  • · Replies 4 ·
Replies
4
Views
2K