What Is Capacitance?
Capacitance is the ability of a device to store electric charge. A capacitor consists of two conducting surfaces separated by an insulating material (dielectric). When voltage is applied, charge accumulates on the plates, creating an electric field.
Capacitance is measured in farads (F). One farad means one coulomb of charge is stored per volt. Since a farad is very large, most practical capacitors are rated in picofarads (pF), nanofarads (nF), or microfarads (μF).
Capacitance Formulas
Basic capacitance from charge and voltage.
Energy stored in a capacitor.
Parallel-plate capacitance.
How to Use the Capacitance Calculator
- 1Choose what to calculate: C, Q, V, Energy, or Parallel-plate.
- 2Enter the required values with appropriate units.
- 3Click Calculate.
- 4Review the formula, substitution, and explanation.
Energy Stored in a Capacitor
Three equivalent forms for capacitor energy. All yield the same result.
Energy increases with the square of voltage. Doubling the voltage quadruples the stored energy. This is why capacitors can deliver sudden bursts of power.
Parallel Plate Capacitance
The simplest capacitor model: two parallel conducting plates of area A separated by distance d. The dielectric between them has relative permittivity εr.
Capacitance increases with area and permittivity, decreases with separation.
Dielectric Materials
| Material | εr | Notes |
|---|---|---|
| Vacuum | 1.0000 | Reference value |
| Air | 1.0006 | Practically same as vacuum |
| Paper | 2.5–3.5 | Used in early capacitors |
| Glass | 4–7 | Good insulator |
| Mica | 5–7 | Precision capacitors |
| PTFE (Teflon) | 2.1 | Low loss, stable |
| Ceramic (high-K) | 200–14000 | Very high C in small size, less stable |
Example Calculations
Basic C = Q/V
Q = 5 μC, V = 10 V. C = 5×10−6 / 10 = 0.5 μF.
Energy stored
C = 100 μF, V = 12 V. E = 0.5 × 100×10−6 × 144 = 7.2 mJ.
Parallel plate
A = 10 cm², d = 1 mm, εr = 1 (vacuum). C = 1 × 8.854×10−12 × 10×10−4 / 10−3 ≈ 8.85 pF.
Types of Capacitors
Common types include ceramic (small, cheap), electrolytic (high capacitance, polarized), film (stable, accurate), tantalum (compact, polarized), mica (precision), and supercapacitors (very high capacitance, low voltage).
Capacitor vs Inductor
| Feature | Capacitor | Inductor |
|---|---|---|
| Stores | Electric field energy | Magnetic field energy |
| Formula | C = Q/V | L = Φ/I |
| Unit | Farad (F) | Henry (H) |
Capacitance Units
1 F = 10³ mF = 10&sup6; μF = 10&sup9; nF = 10¹² pF. Most electronics use pF to μF. Supercapacitors reach farads or even kilofarads.
Where Capacitance Calculations Are Used
Capacitance calculations are used in filter design, energy storage, timing circuits, sensor interfaces, power supply smoothing, decoupling, physics education, and electronics engineering.
Accuracy and Limitations
This calculator uses ideal capacitor formulas. Real capacitors have tolerance, voltage-dependent capacitance (ceramic), equivalent series resistance (ESR), leakage current, and temperature effects. The parallel-plate formula assumes uniform field and infinite plates. This tool is for educational and basic circuit analysis.
Frequently Asked Questions
What is capacitance?›
Capacitance is the ability of a component to store electric charge. It’s defined as C = Q/V, the ratio of charge stored to voltage applied.
What is the unit of capacitance?›
The farad (F). Practical values range from picofarads (pF) to millifarads (mF). One farad stores one coulomb per volt.
How do you calculate capacitance?›
Use C = Q/V if charge and voltage are known, or C = εᵣε₀A/d for a parallel-plate capacitor.
What is a parallel-plate capacitor?›
Two flat conducting plates separated by a dielectric. Capacitance depends on plate area, separation, and the dielectric’s permittivity.
How does a dielectric increase capacitance?›
The dielectric reduces the electric field between plates for the same charge, allowing more charge at the same voltage, thus increasing capacitance by factor εᵣ.
What is ε₀?›
ε₀ (epsilon naught) is the permittivity of free space: 8.854 × 10⁻¹² F/m. It defines how much electric field a vacuum permits.
How much energy does a capacitor store?›
E = ½CV². Energy increases with the square of voltage, so doubling voltage quadruples energy.
Can capacitors replace batteries?›
Supercapacitors can store enough energy for short bursts, but they have lower energy density than batteries. They excel at delivering quick power pulses.
Why are large capacitance values rare?›
Achieving large capacitance requires large plate area, small separation, or high-permittivity dielectrics, all of which are physically or practically limited.
What happens if capacitor voltage is exceeded?›
Exceeding the rated voltage can cause dielectric breakdown, permanent damage, leakage, or catastrophic failure. Always observe voltage ratings.
Sources / References
Author & technical reviewer
Manish Kumar
PhysicsCalcs tools are reviewed with an educational focus: clear formulas, transparent assumptions, and practical context for students and science learners.
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