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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).
Sample Practice Questions

  1. Gauss's law states that total electric flux through a closed surface equals:

    • Q × ε₀
    • Q_enclosed/ε₀
    • ε₀/Q
    • Q/4πε₀
    Show answer

    Answer: Q_enclosed/ε₀

  2. Torque on an electric dipole of moment p in field E at angle θ:

    • pE cosθ
    • pE sinθ
    • pE tanθ
    • p/E sinθ
    Show answer

    Answer: pE sinθ

  3. Coulomb's law: force between two charges q₁ and q₂ at distance r is:

    • kq₁q₂/r
    • kq₁q₂/r²
    • kq₁q₂r²
    • k(q₁+q₂)/r²
    Show answer

    Answer: kq₁q₂/r²

  4. Dielectric constant K is always:

    • Less than 1
    • Equal to 1
    • Greater than 1
    • Zero
    Show answer

    Answer: Greater than 1

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Practice Questions

Practice 20 randomly selected NEET questions on Electrostatics. Answers are revealed after each question.

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