Parasitic Resistance in capacitors/inductors

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Discussion Overview

The discussion revolves around the analysis of parasitic resistance in capacitors and inductors, specifically focusing on a problem involving a capacitor with a given capacitance and parasitic resistance. Participants explore how to determine current amplitudes under specific conditions and consider the implications of similar analysis for inductors.

Discussion Character

  • Homework-related, Technical explanation

Main Points Raised

  • One participant expresses uncertainty about how to approach the problem and what equations are necessary for the analysis.
  • Another participant suggests that the current through the capacitor and the parasitic resistance is equal when the reactance of the capacitor matches the equivalent resistance.
  • A participant later indicates they found a solution but questions how the analysis would change if an inductor were used instead of a capacitor.
  • It is noted that the modeling of inductor losses could vary, with series resistance typically representing copper losses and parallel resistance representing core losses.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the approach for inductors, as the discussion highlights different modeling techniques for losses in inductors.

Contextual Notes

The discussion lacks specific equations or detailed steps for the calculations, and assumptions about the nature of the parasitic resistance in inductors remain unresolved.

dudforreal
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Homework Statement
A 82 nF capacitor has a parasitic parallel resistance Rp = 600 kΩ.
If a voltage V = Vmsin(ωt) is applied, as shown in the diagram, find the frequencies at which:
1. The current amplitude through the parasitic resistance is 1% of the current amplitude
through the capacitor.
2. The amplitudes of the currents through the resistor and the capacitor are equal.


The attempt at a solution

I don't even know where to start with the question and I do not know what equations are needed to get the answer. Any help from people would be great.
 
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The current is equal when the reactance of the capacitance is equal to that of the (equivalent) resistance.

Do you know the formula for capacitive reactance.
 
ok thanks i got the answer but how would you go about it if it was an inductor instead?
 
dudforreal said:
ok thanks i got the answer but how would you go about it if it was an inductor instead?

That would depend upon whether the inductor losses were modeled by a series resistance or an equivalent parallel resistance. Copper losses are usually modeled with a series resistance whereas core loses are usually modeled with an equivalent parallel resistance.
 
ok thanks :smile:
 

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