Key Concepts: Electric Charge & Coulomb’s Law

Electric Charge

• Two types: positive (protons) and negative (electrons). Like charges repel; unlike attract.
• Charge is quantized: comes in multiples of e = 1.6 × 10⁻¹⁹ C.
• Charge is conserved: total charge in an isolated system stays constant.

Coulomb's Law

F = kq₁q₂/r²

• k = 8.99 × 10⁹ N·m²/C² (Coulomb's constant).
• Force is along the line joining the charges.
• Inverse-square law: double the distance → force becomes ¼.

Charging Methods

• Friction: Rubbing transfers electrons between materials.
• Conduction: Direct contact with a charged object.
• Induction: Rearranging charges by bringing a charged object nearby without contact.