Static Electricity & Conduction
Static electricity and the distribution of electrostatic charges; the laws of attraction and repulsion; units of charge and Coulomb's law; conduction in solids, liquids, gases and a vacuum.
Static electricity — summary notes
Free- A body is charged by friction, by contact, or by induction (bringing a charged body near without touching).
- Like charges repel; unlike charges attract. The force obeys Coulomb's inverse-square law.
- The unit of charge is the coulomb: 1 C = 6.24 × 10¹⁸ electrons.
- Conduction happens by different carriers in different media: electrons in solids, ions in liquids and gases, and an electron beam in a vacuum.
- On aircraft, static dischargers (wicks) bleed off precipitation static so it does not build up and interfere with radio and navigation equipment.
- ⚠ Exam trap: force varies as 1/r², not 1/r — double the separation and the force falls to a quarter, not a half.
- Coulomb's law
- F = k·Q₁Q₂ / r² (k ≈ 9 × 10⁹ N·m²/C²)
- Electrons per coulomb
- 1 C = 6.24 × 10¹⁸ electrons
Two charges experience a force of 8 N. If the distance between them is doubled, what is the new force?
F ∝ 1/r². Doubling r divides the force by 2² = 4, so F = 8 / 4 = 2 N.
Why are static wicks fitted to trailing edges?
Flight through precipitation charges the airframe. Wicks provide a high-resistance path with sharp points that bleed the charge back to the atmosphere gradually, preventing a build-up that would discharge as noise across radio and navigation receivers.
Static electricity concept map
FreeStatic Electricity
Static electricity quiz
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