Leydenia

Leydenia, a glass automaton, carries a crackling jar of stored charge: the first capacitor.

The Physics

A Leyden jar is a glass jar with a metal foil coating inside and another outside; the glass between them is the insulator. Charge one foil and an equal and opposite charge gathers on the other. Ewald Georg von Kleist found the effect in 1745, and Pieter van Musschenbroek at Leiden independently in 1746, which is how it got its name. The jar's capacitance is how much charge it holds per volt.

C = Q/V

• C: capacitance (farad, F)
• Q: charge on each foil, equal and opposite (C)
• V: voltage between the foils (V)

The energy stored is ½CV², and the sudden discharge of one was enough to give early experimenters a painful shock.

Honest caveat: The charge sits on the foils, not in the glass; the glass only keeps them apart and raises C. A jar's capacitance is small, typically around a nanofarad.

On the sticker

Leydenia holds up a glowing glass jar with a metal band at its base and blue sparks inside. Printed text: LEYDENIA with the line C = Q/V. Pixel-art kiss-cut vinyl sticker, white, in 2″, 3″, 4″ and 6″ sizes.