Subject overview
Capacitors
Charge, stored energy, plate geometry, electric fields, AC circuits and RC transients.
01 Capacitors: Series & Parallel
Variables
- C1capacitance 1
- Ffarad
- C2capacitance 2
- Ffarad
- nnumber of capacitors
- 1dimensionless
- Cparallel equivalent capacitance
- Ffarad
Key Formulas
For constant capacitance, current is the time derivative of charge. Integrating voltage against transferred charge gives stored energy. In an RC circuit, Kirchhoff’s voltage law produces a first-order differential equation with time constant RC.
Ideal positive capacitances. Complete the visible capacitances to add the next optional field. The empty final field is not included.
Calculate
Type prefixes directly: 1.5k, 250m or 20u. Results: 3 significant figures.
Ideal positive capacitances. Complete the visible capacitances to add the next optional field. The empty final field is not included.
Enter the required input values to calculate.
02 Capacitor Calculations
Variables
- Icurrent
- Aampere
- Fforce component
- Nnewton
- Eelectric field strength
- V/mvolts per meter
- εᵣrelative permittivity
- 1dimensionless
- Aplate area
- m²square meter
- dplate diameter
- mmeter
- splate separation
- mmeter
- Ccapacitance
- Ffarad
- Uvoltage
- Vvolt
- Wstored energy
- Jjoule
- Qcharge
- Ccoulomb
- ttime interval
- ssecond
Key Formulas
For constant capacitance, current is the time derivative of charge. Integrating voltage against transferred charge gives stored energy. In an RC circuit, Kirchhoff’s voltage law produces a first-order differential equation with time constant RC.
Ideal linear parallel-plate capacitor with uniform dielectric and field. Edge effects and dielectric breakdown are neglected. Time-related charge and current are mean changes over t. Circular plate geometry uses diameter d; plate separation is s. ε₀ = 8.8541878188 × 10⁻¹² F/m.
Calculate
Type prefixes directly: 1.5k, 250m or 20u. Results: 3 significant figures.
Ideal linear parallel-plate capacitor with uniform dielectric and field. Edge effects and dielectric breakdown are neglected. Time-related charge and current are mean changes over t. Circular plate geometry uses diameter d; plate separation is s. ε₀ = 8.8541878188 × 10⁻¹² F/m.
Enter the required input values to calculate.
03 RC at AC: Series & Parallel
Variables
- φphase angle
- radradian
- Itotal RMS current
- Aampere
- Rresistance
- Ωohm
- XCcapacitive reactance
- Ωohm
- Zimpedance magnitude
- Ωohm
- Ccapacitance
- Ffarad
- Pactive power
- Wwatt
- QCcapacitive reactive power
- varvar
- Sapparent power
- VAvolt-ampere
- URresistive voltage
- Vvolt
- UCcapacitive voltage
- Vvolt
- Utotal RMS voltage
- Vvolt
- ffrequency
- Hzhertz
- cos(φ)power factor
- 1dimensionless
- sin(φ)reactive factor
- 1dimensionless
- IRresistive branch current
- Aampere
- ICcapacitive branch current
- Aampere
Key Formulas
For constant capacitance, current is the time derivative of charge. Integrating voltage against transferred charge gives stored energy. In an RC circuit, Kirchhoff’s voltage law produces a first-order differential equation with time constant RC.
Switch between series and parallel RC connection. Series uses partial voltages U_R and U_C; parallel uses branch currents I_R and I_C. Enter any independent known quantities; the calculator derives every uniquely determined missing value. U and I are RMS; φ, sin(φ) and Q_C are negative for a capacitive load.
Calculate
Type prefixes directly: 1.5k, 250m or 20u. Results: 3 significant figures.
Ideal sinusoidal steady state. U and I are RMS values. The phase angle, reactive factor and capacitive reactive power are negative. R, X_C, Z, C and f are positive.
Enter the required input values to calculate.
Schematic curve; no numerical scale.
04 RC: Charging & Discharging
Variables
- Isupply current
- Aampere
- i(t)instantaneous current
- Aampere
- τtime constant
- ssecond
- Rresistance
- Ωohm
- Ccapacitance
- Ffarad
- Usupply voltage
- Vvolt
- u(t)instantaneous voltage
- Vvolt
- telapsed time
- ssecond
Key Formulas
For constant capacitance, current is the time derivative of charge. Integrating voltage against transferred charge gives stored energy. In an RC circuit, Kirchhoff’s voltage law produces a first-order differential equation with time constant RC.
Switch between charging from an ideal DC step and discharging an initially charged capacitor through R. Every listed quantity can be entered; uniquely determined missing values are calculated. R, C and τ > 0; t ≥ 0. Inputs remain available when the process changes.
Calculate
Type prefixes directly: 1.5k, 250m or 20u. Results: 3 significant figures.
Ideal DC step U at t = 0, zero initial stored energy. I = U/R is the initial supply current. R, C and τ > 0; t ≥ 0.
Enter the required input values to calculate.
Schematic curve; no numerical scale.
Schematic curve; no numerical scale.