Capacitor Charge

Formula

Description

This is the defining equation of capacitance: the charge stored on a capacitor is directly proportional to the voltage applied across it. One farad is defined as one coulomb of charge per volt. In practice, most capacitors store microcoulombs or nanocoulombs of charge. The relationship is linear for ideal capacitors, meaning doubling the voltage doubles the stored charge. Current flowing into a capacitor is the rate of change of charge: I = dQ/dt = C × dV/dt, which is why capacitors block DC and pass AC.

Variables

• Q — Charge in coulombs (C)
• C — Capacitance in farads (F)
• V — Voltage across the capacitor (V)

Practical Notes

One coulomb is an enormous amount of charge in electronics terms, equivalent to 6.24 × 10^18 electrons. A typical 100µF capacitor charged to 5V holds 500µC. The concept of charge conservation is central to Kirchhoff's Current Law and charge-based circuit analysis.