Kappon

Meet Kappon, an insulating slab who slips between capacitor plates and lets them hold more charge.

A capacitor stores charge on two plates separated by a gap. If you slide an insulating material into that gap, the molecules inside it stretch or twist slightly in the electric field. Their charges line up so that they partly cancel the field between the plates.

With a weaker field for the same charge, the voltage drops, so the capacitor can store more charge at a given voltage. The new capacitance is C = κC₀, where κ is the dielectric constant of the material. A material with κ = 5 turns a 10 pF capacitor into a 50 pF capacitor. Pure water has κ of about 80.

A dielectric also helps stop sparks jumping between the plates, so the capacitor can survive higher voltages.

Nearly every real capacitor uses one. Ceramics, plastic films and thin oxide layers are all dielectrics chosen to pack a lot of capacitance into a small space.