Static Electricity and Conduction
Static electricity and conduction questions test how charge accumulates, how it moves, and how aircraft wiring and refuelling practice control it. You must distinguish charging by friction from induction, explain conduction in solids and electrolytes, and recognise electrostatic discharge hazards.
Core rules
- Like charges repel, unlike charges attract; force follows Coulomb's law, F = kQ1Q2/r².
- Friction transfers electrons between materials, leaving one positive and one negative.
- Induction redistributes charge on a conductor without contact; the conductor can then be grounded to remove the separated charge.
- Electric field lines point from positive to negative and are strongest where lines are closest.
- Conduction needs mobile charge carriers: electrons in metals, ions in electrolytes.
- Bonding connects aircraft and fuel equipment to equalise potential; earthing connects to earth ground. Static dischargers bleed in-flight charge.
Worked example
Two point charges of +2 µC and +3 µC are 0.10 m apart in air. Find the force. F = kQ1Q2/r² = (9 × 10^9 × 2 × 10^-6 × 3 × 10^-6) / (0.10)² = (9 × 10^9 × 6 × 10^-12) / 0.01 = 0.054 / 0.01 = 5.4 N. Because the charges are alike, the force is repulsive.
Traps
- Saying static charge is current; static is charge at rest.
- Confusing bonding with earthing: bonding equalises two objects, earthing references them to ground.
- Assuming all liquids conduct like metals; pure water is a poor conductor, electrolytes conduct by ions.
- Forgetting that induction requires no contact and no transfer of charge.