Static Electricity and Conduction
Static charge
Static electricity is charge at rest, produced by triboelectric separation - rubbing dissimilar materials transfers electrons so one surface becomes positive and the other negative. Charge resides on the outer surface of a conductor and distributes so that the internal field is zero (the Faraday cage effect). Like charges repel; Coulomb's law gives the force: F = kQ₁Q₂/r² with k ≈ 9 x 10⁹ N m² C⁻². Double the separation and the force falls to one quarter.
Electric field strength E = V/d (volts per metre). Charge concentrates at sharp points, producing high potential gradients and corona discharge; this is why aircraft carry static dischargers (wicks) on trailing edges to bleed charge away and protect radio reception.
Conduction
Conduction requires mobile charge carriers: electrons in metals, ions in electrolytes, and ions plus electrons in gases - a gas must be ionised before it conducts (a spark). Conductance G = 1/R, measured in siemens.
Aircraft practice
Static is a real hazard: refuelling requires bonding of the aircraft to the fuel bowser and to earth, preventing a spark igniting fuel vapour. Bonding equalises potential between two items; earthing connects to the ground reference. Composite aircraft need conductive mesh or foil to dissipate lightning and static.
Traps
- Bonding is not earthing; questions deliberately swap them.
- Charge on a conductor sits on the outside surface, not throughout the volume.
- Static charges are tiny in coulombs but can reach many kilovolts.
- Lightning protection and static discharge wicks are related but not the same thing.