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In addition to the revision notes for RC Circuits on this page, you can also access the following Electrodynamics learning resources for RC Circuits
| Tutorial ID | Title | Tutorial | Video Tutorial | Revision Notes | Revision Questions | |
|---|---|---|---|---|---|---|
| 15.7 | RC Circuits |
In these revision notes for RC Circuits, we cover the following key points:
A RC circuit is the combination of a pure resistance R in ohms and a pure capacitance C in Farads. The capacitor stores energy while the resistor connected in series with the capacitor controls the charging and discharging process in the capacitor.
The charging process of capacitor does not occur in a uniform rate. This is because more the capacitor is charged, more the like charges repel each other. As a result, the charging process becomes more difficult towards the end of cycle. This process progressively slows down until it eventually stops when the capacitor is fully charged. This means the charging process is not linear but it contains a negative exponential term.
The equation which calculates the change in electric potential difference in terms of the time elapsed when charging a capacitor C through a resistor R, is
where ε is the electromotive force generated by a DC source (for example a battery).
The term R ∙ C in the fraction denominator has the unit of time (second). We can write this term by τ; it shows how fast the circuit is charging or discharging.
Some of the properties of capacitors connected in RC circuits include:
The discharge of a capacitor in a RC circuit is the inverse process of capacitor charging. Therefore, we obtain a decreasing exponential function when considering the potential difference vs time variation. The equation of potential difference of a capacitor during the discharge process is
Since potential difference is proportional to the charge stored in a capacitor, the amount of charge remained in a capacitor after t second of discharge is
where Q0 is the initial charge stored in the capacitor when it is charged at maximum and Q(t) is the charge in the capacitor at the instant t.
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