RC Time Constant & Capacitor Charging Calculator (τ = RC)
Calculate RC circuit time constant tau (τ = RC), capacitor charge and discharge voltage V(t), 5τ full charge duration, and -3dB cutoff frequency.
Calculated Results
Frequently Asked Questions
What is the RC time constant (tau)?
The time constant tau (τ = R × C) represents the time in seconds required for a capacitor to charge to approximately 63.2% of its maximum supply voltage through a resistor, or discharge down to 36.8% of its initial voltage.
Why does it take 5 time constants (5τ) to fully charge a capacitor?
Capacitor charging follows an asymptotic exponential curve V(t) = V0(1 - e^(-t/tau)). At 1τ it reaches 63.2%; at 2τ: 86.5%; at 3τ: 95.0%; at 4τ: 98.2%; and at 5τ: 99.3%, which is considered fully charged in practical electrical engineering.
What is the cutoff frequency of an RC filter circuit?
In audio and signal processing, a simple RC network acts as a passive low-pass or high-pass filter. The -3dB cutoff frequency is calculated as: fc = 1 / (2π × R × C).
How does resistance impact capacitor discharge time?
Higher resistance restricts electric current flow, increasing tau and prolonging discharge time. Lower resistance allows rapid charge/discharge, which is why bleed resistors on high-voltage power supplies must be properly sized.