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Current in RC circuit
Intermediate
Charging current decays exponentially.
I = (V/R)e^{−t/RC}Initially the full V₀/R flows (capacitor acts like a short), decaying to zero as the capacitor charges and becomes an open circuit.
At t = τ I = 0.37 I₀.
Different from the capacitor voltage curve.
In more detail
In an RC circuit, the current is I = (V/R) e^(−t/RC) during charging, starting at its maximum value and decaying exponentially as the capacitor fills.
Real-world uses
- Circuit analysis uses current decay to predict transient behaviour.
- Protecting components by limiting inrush current.
- When a capacitor starts charging, the current through the resistor is largest and then decays as the capacitor fills.
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Frequently asked questions
What is the initial current?
V divided by R, when the capacitor is still uncharged.
When does current become negligible?
After several time constants.
Why does the current drop as the capacitor charges?
The capacitor voltage opposes the supply, so the net driving voltage across the resistor shrinks.
Related topics in Current Electricity & Circuits
RC circuit charging · RC circuit discharging · Time constant · Capacitor networks · Diodes · Rectifier circuits