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
- 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
Static Electricity
Static electricity quiz
Static Electricity & Conduction, quiz
1. Two like charges placed near each other will:
Repel each otherAttract each otherHave no effect2. Static bonding leads on an aircraft are fitted to:
Give static charge a safe path to dissipateIncrease the aircraft weightImprove radio reception only3. Two charges experience a force F. If the distance between them is doubled, the force becomes:
F/4F/22F4. Like electrical charges:
Repel each otherAttract each otherHave no effect on each other5. One coulomb of charge is equivalent to approximately:
6.24 × 10¹⁸ electrons1.6 × 10⁻¹⁹ electrons9 × 10⁹ electrons6. In a liquid electrolyte, conduction takes place by the movement of:
IonsFree electrons onlyPhotons7. Static dischargers (wicks) are fitted to an aircraft to:
Bleed off precipitation static and prevent radio interferenceIncrease the aircraft's electrical capacityProvide a path for lightning to enter the airframe8. Charging a body by bringing a charged object near it without contact is called charging by:
InductionFrictionConduction9. The constant k in Coulomb's law is approximately:
9 × 10⁹ N·m²/C²6.24 × 10¹⁸ N·m²/C²1.6 × 10⁻¹⁹ N·m²/C²10. Conduction in a vacuum takes place by:
An electron beamIon movementIt cannot occur at all11. If the charge on one of two bodies is doubled, the force between them:
DoublesQuadruplesHalves12. Rubbing two dissimilar insulating materials together produces charge by:
FrictionInductionChemical action