A capacitor stores energy in an electric field between two conductors separated by an insulating material (dielectric). The key relation is Q = C·V, meaning stored charge Q grows with capacitance C and voltage V.

Charging, discharging, and RC timing

In a simple RC circuit, capacitor voltage rises exponentially while charging and falls exponentially while discharging. The time constant is τ = R·C. As a practical rule, after about 5τ the capacitor is considered almost fully charged or discharged.

What capacitors do in real circuits

  • Power smoothing: reduce ripple after rectification.
  • Decoupling/bypass: supply short bursts of current near IC pins and suppress noise.
  • Timing networks: set delays, pulse widths, and oscillator behavior with resistors.
  • Energy buffering: support camera flash circuits, motor starts, and hold-up power.

Stored energy is E = 1/2·C·V². That is why even moderate capacitance at high voltage can store meaningful energy and must be handled carefully in design and maintenance.