Capacitance (C = Q/V)

Capacitance is charge-storing capacity: how many coulombs a capacitor soaks up for every volt you apply across it. The unit, the farad, honors Michael Faraday — and it is a giant. A full farad would have been a bench-filling curiosity for most of electronics history, so practical parts are marked in microfarads, nanofarads, and picofarads; only modern supercapacitors reach whole farads. Doubling the applied voltage doubles the stored charge, but C itself stays fixed — it depends only on geometry and the insulating material between the plates.

Worked example: a 100 µF capacitor charged to 12 V holds Q = CV = 100×10⁻⁶ × 12 = 1.2 mC of charge — about 7.5×10¹⁵ electrons parked on one plate and missing from the other. This defining relation applies to every capacitor, from the tuning capacitor in a radio to the DRAM cell storing one bit in your computer.