The physics
A capacitor is two conductors that hold equal and opposite charges. Its charge grows in step with the voltage across it.
Q = C V U = ½CV² = Q²/2C = ½QV
The capacitance C depends only on the capacitor's shape and size.
plates: C = ε0A/d sphere: C = 4πε0R
two spheres, one centre: C = 4πε0ab/(b − a) cable: C per metre = 2πε0/ln(b/a)
Capacitors in a line (in series) all hold the same charge. Side by side, they all share one voltage.
series: 1/C = 1/C₁ + 1/C₂ side by side: C = C₁ + C₂
Use ε0 = 8.85 × 10⁻¹² F/m for plates and cables, and k = 1/4πε0 = 9 × 10⁹ N m²/C² for spheres.