Capacitors in Circuits: Is Current Ignored?

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Discussion Overview

The discussion revolves around the behavior of capacitors in electrical circuits, particularly focusing on whether current can be ignored in fully charged capacitors within DC and AC contexts. Participants explore the implications of capacitor charging on circuit analysis and the conditions under which current may or may not flow.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant suggests that in a fully charged capacitor within a DC circuit, current can be ignored, while another points out that this is not the case in AC circuits where capacitors function as high pass filters.
  • Another participant emphasizes the importance of analyzing circuits even with fully charged capacitors, noting that unexpected behaviors can occur, especially if the capacitor's voltage exceeds that of the supply.
  • A participant inquires about the relevance of these concepts while learning DC circuits and asks how to analyze circuits with partially charged capacitors.
  • It is mentioned that in a steady state DC scenario, a fully charged capacitor behaves like an open circuit, but any changes in the circuit necessitate its inclusion in analysis.
  • One participant proposes using the equation q=VC for analyzing charge in capacitors, while also referencing impedance in AC circuits, indicating a need for frequency considerations.

Areas of Agreement / Disagreement

Participants express differing views on the treatment of fully charged capacitors in circuit analysis, particularly between DC and AC scenarios. There is no consensus on whether current can be ignored in all cases, and the discussion remains unresolved regarding the implications of partially charged capacitors.

Contextual Notes

Participants mention various conditions under which capacitors should be considered in circuit analysis, including steady state conditions and changes in circuit configuration. The discussion highlights the need for clarity on definitions such as "fully charged" and the implications of voltage levels.

Who May Find This Useful

This discussion may be useful for students learning about circuit analysis, particularly those focusing on the role of capacitors in both DC and AC circuits, as well as individuals interested in the nuances of electrical engineering concepts.

darksyesider
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If a capacitor is fully charged in a circuit, am I correct in saying that you can ignore that section of the circuit because no current goes through/leaves it?
 
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In DC, yea, pretty much, but not in AC. In AC circuits they act as high pass filters.
 
I would still math it out, just because some circuits can do weird things, but most caps can handle upwards of a couple hundred volts, and if it's "fully charged" you're either saying: 1 it's in equilibrium with the voltage supply, or 2 it's at a higher voltage then your voltage supply, so current flows backwards, unless you have a huge supply.
 
I am only learning DC right now, so do I still need to worry about that?

Also, if you have a capacitor that is not fully charged, how would you analyze the circuit then?
 
IN the case of DC - and in a steady state - nothing changing, once the cap is charged, it "looks" like an open circuit. As soon as anything changes in time, the capacitor needs to be considered.
So when you say not fully charged - what do you mean, charged to it's maximum voltage - or you change something in the circuit like close a switch? For example - at Time 0 the cap is at 2 V and then something changes and the capacitor may charge to 6V... this is still a DC case, but the Capacitor needs to included in your analysis.
 
I'm pretty sure you'll want to use q=VC for it. Charge stored in the capacitor = voltage across the capacitor time its capacitance. If its not, sorry, I haven't analyzed DC circuited in forever. The only other equation coming to mind is the impedence, but that requires a frequency. Z=1/iwc in AC you use both, q for time dependent analysis, and z for complex analysis. Hope this helps, if not Google is your best friend, I'd look but I'm on my Droid now
 

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