Electric Charge & Coulomb’s Law — A/L Physics

What must I remember about Electric Charge & Coulomb’s Law?

• Electric Charge Properties: Two types of charge (positive and negative); Like charges repel, opposite charges attract; Quantization of charge: Q = ± n e, where elementary charge e = 1.602 × 10⁻¹⁹ C; Conservation of charge: Total charge in an isolated system remains strictly constant.
• Coulomb's Law: Electrostatic force between two stationary point charges in vacuum: F = (1 / (4πε0)) * (|q1 q2| / r²), where ε0 is permittivity of free space (8.854 × 10⁻¹² F/m), and 1 / (4πε0) ≈ 8.99 × 10⁹ N·m²·C⁻².
• Dielectric Medium Effect: In a medium of relative permittivity (dielectric constant) ε_r: Permittivity ε = ε_r ε0; Force in medium F_med = F_vacuum / ε_r (force is reduced by factor ε_r).
• Principle of Superposition: Net electrostatic force acting on any target charge is the vector sum of individual Coulomb forces exerted on it by all surrounding charges independently: F_net = ∑ F_i.

Test yourself (1 minute)

1. Point Charge Limitation

   Coulomb's inverse square law applies strictly to point charges or non-overlapping spherically symmetric charge distributions (by Shell Theorem).

2. Electrostatic vs Gravitational Force

   For two electrons: F_e / F_g ≈ 10⁴²; electrostatic force is enormously stronger than gravity at atomic scales, but gravity dominates cosmically due to net electrical neutrality.

3. Vector form of Coulomb's Law

   F₁₂ = (1 / (4πε0)) * (q1 q2 / r²₁) * r̂₂₁.

Practise Electric Charge & Coulomb’s Law questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 6: Electrostatic Field

What should I study first?

What comes next?

Next in the syllabus

Where does Electric Charge & Coulomb’s Law fit in the syllabus?

Unit 6.1 · Year 1 · Term 3