How Does Increasing Frequency Affect Capacitor Voltage in an RC Circuit?

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    Capacitor Voltage
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Discussion Overview

The discussion revolves around the effects of increasing frequency on the voltage across a capacitor in an RC circuit. Participants explore theoretical implications, mathematical relationships, and practical considerations related to AC voltage sources and capacitor behavior across various frequencies.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning
  • Experimental/applied

Main Points Raised

  • Some participants suggest that increasing the frequency will lower the impedance of the capacitor, leading to a decrease in voltage across it, particularly at very high frequencies.
  • Others argue that at moderate frequencies, the capacitor may still have a significant voltage across it, and the relationship can be understood through voltage division.
  • A participant questions whether the impedance formulas for capacitors and inductors apply to non-sinusoidal waveforms, such as square and sawtooth waves, and another confirms that these formulas can be used with such waveforms if decomposed into sine components.
  • One participant emphasizes the importance of understanding reactance versus impedance and provides formulas for both, while another participant challenges the notion that a capacitor across an AC supply will "short" the supply, suggesting it provides a complex load instead.
  • Concerns are raised about potential damage to voltage sources when capacitors are connected in parallel at high frequencies, with some participants noting that the actual behavior would depend on the protective circuitry present.
  • There is a discussion about the behavior of ideal components versus real components, with one participant noting that real capacitors behave differently at high frequencies due to parasitic effects.

Areas of Agreement / Disagreement

Participants express a range of views regarding the implications of frequency on capacitor behavior, with no clear consensus on the effects of high frequencies on voltage across capacitors or the interpretation of impedance versus reactance. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Limitations include assumptions about ideal components versus real-world behavior, the need for Fourier analysis to apply certain formulas to complex waveforms, and the dependency of circuit behavior on protective circuitry that may not be present in all scenarios.

  • #31
I agree completely with you Jim...I am also a 'child of the 60s'.I fully recognise the application and value of complex numbers in physics. But I would still emphasise that they are a mathematical tool, they are not essential and at the level I teach (A level +) a full understanding of the behaviour of AC circuits can be obtained with straight forward geometrical vector diagrams ...the next step to using complex notation is easy but there is not time to go into that in the physics course.
I very much appreciate your comments, not just in this thread but in your excellent posts regarding electronics...I recognise your 60s background in what you write !
 
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  • #32
I recognize your lack of background in what you write. Please read the wikipedia entry on Impedance.
 
  • #33
technician said:
a full understanding of the behaviour of AC circuits can be obtained with straight forward geometrical vector diagrams

Yes, that is how one does analysis of complex quantities.
 
  • #34
technician said:
... a full understanding of the behaviour of AC circuits can be obtained with straight forward geometrical vector diagrams ...the next step to using complex notation is easy but there is not time to go into that in the physics course...

Indeed in only a one or two semester general physics course I see why you don't go into it.

My high school had a 2 hour per day three year almost vo-tech electronics course, but with more math than prior vocational curricula. Our school board was reacting to Sputnik and tried out a few pre-engineering high school courses. So we had plenty of time to learn and drill complex arithmetic. I must say I likely would not have made it through EE school without the practical background from that electronics course. Familiarity with rotating phasor notaion made 3 phase seem natural.

Thanks for the kind words...

Your practical teachings will doubtless influence some kids.

old jim
 

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