Capacitta

Meet Capacitta, two metal plates holding opposite charges close together and storing energy in the field between them.

Put charge +Q on one plate and −Q on the other and a nearly uniform electric field fills the gap. Capacitance C measures how much charge the pair holds per volt of potential difference. For flat plates in vacuum it is ε₀A/d: bigger plates hold more charge, and a smaller gap makes the voltage lower for the same charge, so the capacitance rises.

Example: two 10 cm × 10 cm plates 1 mm apart in vacuum have C ≈ 8.85×10⁻¹² × 0.01 / 0.001 ≈ 89 picofarads. The stored energy is ½CV².

Capacitors smooth power supplies, store the energy for camera flashes and defibrillators, and sense touch in phone screens.

The formula ignores fringe fields at the edges, so it is best when the gap is small compared with the plates. Filling the gap with an insulator, a dielectric, raises C by its dielectric constant.