Capacitance Formula
Learn the capacitance formula C = Q/V and how capacitors combine in series and parallel.
Essential for circuit design and energy storage.
The Formula
Capacitance measures a capacitor's ability to store electric charge.
A higher capacitance means the component can store more charge at a given voltage.
The SI unit is the Farad (F), but most practical capacitors are measured in microfarads (μF), nanofarads (nF), or picofarads (pF).
Variables
| Symbol | Meaning |
|---|---|
| C | Capacitance (Farads, F) |
| Q | Stored charge (Coulombs, C) |
| V | Voltage across the capacitor (Volts, V) |
Series and Parallel Rules
Capacitors in series (total capacitance decreases):
Capacitors in parallel (total capacitance increases):
Example 1
A capacitor stores 0.006 C of charge at 12 V. What is its capacitance?
C = Q / V
C = 0.006 C / 12 V
C = 0.0005 F = 500 μF
Example 2
Two capacitors, 10 μF and 15 μF, are connected in series. What is the total capacitance?
1/C_total = 1/C₁ + 1/C₂
1/C_total = 1/10 + 1/15
1/C_total = 3/30 + 2/30 = 5/30
C_total = 30/5
C_total = 6 μF
When to Use It
Use the capacitance formula when you need to:
- Determine how much charge a capacitor can store
- Calculate the voltage across a charged capacitor
- Combine capacitors in series or parallel circuits
- Design timing circuits, filters, and power supplies
Energy stored in a capacitor is E = ½CV².
Note that capacitor combination rules are the opposite of resistor rules: capacitors in parallel add directly, while those in series use the reciprocal formula.