Electrostatics

Coulomb's law, electric field, potential, capacitors

Key Concepts
  • Coulomb's law: force between point charges
  • Electric field lines originate from positive, terminate at negative charges
  • Electric potential: work done per unit charge to bring test charge from infinity
  • Gauss's law: total flux through closed surface = Q_enclosed / ε₀
  • Electric field inside a conductor is zero; potential is constant
Important Formulae
Coulomb's force F = kq₁q₂/r²; k = 9×10⁹ N·m²/C²
Electric field E = kq/r²
Electric potential V = kq/r
Capacitance (parallel plate) C = ε₀A/d
Energy stored in capacitor U = ½CV² = Q²/2C
Gauss's law ∮E·dA = Q_enc/ε₀
Quick Tips
  • Capacitors in series: 1/C_eff = Σ(1/Cᵢ); in parallel: C_eff = ΣCᵢ.
  • Dipole: p = qd; torque τ = pE sinθ; potential energy U = −pE cosθ.
  • Dielectric increases capacitance by factor κ (dielectric constant).
Practice Questions

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