Capacitance Formula
Calculate capacitance, charge stored, and energy in a capacitor.
Covers parallel plate capacitors.
The Formulas
Capacitance: C = Q / V
Parallel Plate: C = ε₀ × A / d
Energy Stored: E = ½ × C × V²
Parallel Plate: C = ε₀ × A / d
Energy Stored: E = ½ × C × V²
Capacitance measures a capacitor's ability to store electric charge. A larger capacitance means more charge can be stored at the same voltage.
Variables
| Symbol | Meaning | Unit |
|---|---|---|
| C | Capacitance | Farads (F) |
| Q | Charge stored | Coulombs (C) |
| V | Voltage across the capacitor | Volts (V) |
| ε₀ | Permittivity of free space (8.854 × 10⁻¹² F/m) | F/m |
| A | Area of each plate | m² |
| d | Distance between plates | m |
| E | Energy stored | Joules (J) |
Example 1
A capacitor stores 0.006 C at 12 V. What is the capacitance?
C = Q / V = 0.006 / 12
= 0.0005 F = 500 μF
Example 2
How much energy does a 100 μF capacitor store at 50 V?
E = ½ × C × V² = 0.5 × 0.0001 × 50²
= 0.5 × 0.0001 × 2500
= 0.125 J
When to Use It
Use the capacitance formula when:
- Designing electronic circuits with capacitors
- Calculating energy stored in capacitor banks
- Analyzing timing circuits (RC circuits)
- Understanding camera flashes, defibrillators, and other charge-discharge devices