Question

Do the equations for charging and disharging capacitors always apply?Do the formulas for adding capacitors in series and parallel give accurate results?

Answer 1

Yes, the equations for charging and disharging capacitors are always apply. These are derived using Kirchoff’s loop rule. Basically we set up an RC circuit, either with a battery for a charging case, or with a conducting path between capacitor plates for a discharging case.

If a battery (which enforces a potential difference) is newly connected to an RC circuit, then the capacitor will charge up. In this case the appropriate equations are the charging ones. If something happens to allow charge to flow back from one plate of a charged-up capacitor to the other, e.g. a switch is thrown to “short out” the battery, so that the battery no longer enforces a potential difference across the capacitor, then it’s a discharging situation and the discharging equations are the ones that describe it.

In theory the formulas for adding capacitors in series and parallel give accurate results but in practical when we use more number of capacitor in combination we face challanges. When two capacitors are used in series, then the issue is often that the two capacitors do not share the voltage equally. Differences in leakage current occur between capacitors, especially for capacitors like electrolytic versions and this means that the voltages across the two capacitors can differ greatly, and as a result one may be subject to an over-voltage conditions which could result in the destruction of one or both capacitors.

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