Technology
RC low-pass cutoff
Calculate the time constant and cutoff frequency of a first-order RC low-pass filter, whose cutoff has approximately 70.7% of the input voltage amplitude.
Calculators / Science / RC voltage after a step
RC voltage after a step calculator
Estimate capacitor voltage and resistor current after a constant source-voltage step.
On this page
Capacitor voltage7.59V
Resistor current4.41e-3A
Time constant0.1s
Calculator controls
How to calculate
Estimate capacitor voltage and resistor current after a constant source-voltage step.
Capacitor voltage =
Vs+(V0-Vs)*exp(-t/(R*C/1000000)) VResistor current =
(Vs-(Vs+(V0-Vs)*exp(-t/(R*C/1000000))))/R ATime constant =
R*C/1000000 sWorked example
- Resistance (Ω): 1000
- Capacitance (µF): 100
- Final source voltage (V): 12
- Initial capacitor voltage (V): 0
- Elapsed time (s): 0.1
- Capacitor voltage: 7.59 V
- Resistor current: 4.41e-3 A
- Time constant: 0.1 s
Assumptions and limits
This is an ideal educational model. Enter quantities in the stated SI units; it does not certify equipment safety or real operating limits. Uses one ideal resistor and capacitor, with a fixed source after t = 0; leakage and parasitic effects are excluded.
Results are rounded for display; calculations use unrounded values. Read our calculation methodology.
Understanding the result
Estimate capacitor voltage and resistor current after a constant source-voltage step. Use a zero final source to model discharge or a higher final source to model charging. Initial voltage need not be zero.
When this tool is useful
Use a zero final source to model discharge or a higher final source to model charging. Initial voltage need not be zero.
Understanding your inputs
| Input | Example |
|---|---|
Resistance (Ω) R | 1000 |
Capacitance (µF) C | 100 |
Final source voltage (V) Vs | 12 |
Initial capacitor voltage (V) V0 | 0 |
Elapsed time (s) t | 0.1 |
Frequently asked questions
Which assumptions matter for this result?
This is an ideal educational model. Enter quantities in the stated SI units; it does not certify equipment safety or real operating limits. Uses one ideal resistor and capacitor, with a fixed source after t = 0; leakage and parasitic effects are excluded.
How can I check the worked example?
Use the displayed example inputs in the stated formula. Keep each quantity in its labelled unit and compare the unrounded result before applying display rounding.