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RC time constant calculator

τ = RC, charging time and cut-off frequency.

Try the circuit in the labBuild it on the simulator's bench and measure it.

How it is worked out

A capacitor charging through a resistor follows V(t) = Vs(1 − e−t/RC). After one time constant τ = RC it is at 63 %, after 5τ it is practically full (99.3 %). Discharging is the mirror image.

Example: 10 kΩ and 100 µF give τ = 1 s, so the capacitor is effectively charged after 5 s.

The same pair makes a low-pass or high-pass filter with its −3 dB corner at fc = 1 ÷ (2πRC).

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