Calculate the time constant, energy, and charge for a resistor-capacitor (RC) circuit.
Last updated: March 2026 | By ForgeCalc Engineering
An RC circuit is an electrical circuit composed of resistors and capacitors. It is one of the most fundamental building blocks in electronics, used for filtering, timing, and energy storage.
The Time Constant (τ) is the time required to charge the capacitor, through the resistor, to approximately 63.2% of its full charge. After 5 time constants (5τ), the capacitor is considered fully charged (99.3%).
Time constant in seconds.
Stored energy in Joules.
For a simple RC filter, the cutoff frequency (f_c) is 1 / (2πRC). This is the point where the signal power is reduced by half.
Mathematically, it takes infinite time, but for practical engineering, we use 5 time constants (5τ) as the 'fully charged' point.
Yes, but the behavior is more complex. In AC, the capacitor has 'reactance' (X_c = 1 / 2πfC) which varies with frequency.
The unit is the Coulomb (C). One Coulomb is the charge transported by a constant current of one ampere in one second.
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