Physics
Capacitor Discharge Calculator
Model an ideal capacitor discharging through a resistor with V = V₀e⁻ᵗ/τ and τ = RC.
Your measurements
Start with the example, or enter your own values. Use a dot for decimals and e for scientific notation.
Calculated locally. No account or uploads.
Result & working
ExampleThe calculator is loading. You can read the worked example below.
Step-by-step working
The formula
V = V₀e^(−t/τ)
t = −τ ln(V/V₀)
τ = −t / ln(V/V₀)
t₁/₂ = τ ln 2
| Symbol | Meaning |
|---|---|
| V₀ | Initial capacitor voltage. |
| V | Voltage after elapsed time t. |
| τ | Time constant RC in seconds. |
When to use this calculator
Use this for an ideal first-order RC discharge with constant R and C and negligible meter loading.
A plot of ln V against t should be linear with gradient −1/RC when the model is appropriate.
Worked example
The calculator opens with these example values. All steps below are available even with JavaScript disabled.
- V = V₀e^(−t/τ)
- = 5 × e^(−1/1) = 1.839397 V
1.839397 V
Common mistakes
- For discharge, 0 < V ≤ V₀.
- Do not use log base 10 in the exponential law unless you convert the slope appropriately.
- Real leakage, meter resistance and component tolerances can affect the measured curve.