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Electric fields arise from electric charges and are responsible for the forces between charged particles. This topic draws many parallels with gravitational fields but includes some key differences — most notably that the electric force can be repulsive as well as attractive. The capacitor section builds on the principles of electric fields to explain charge storage, energy storage, and exponential charge/discharge behaviour. This material is tested in AQA Paper 2 (Section 7) and OCR Paper 1 (Module 5).
Key Definition: Coulomb's Law states that the force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
F = kQ₁Q₂/r² = Q₁Q₂/(4πε₀r²)
where k = 1/(4πε₀) ≈ 8.99 × 10⁹ N m² C⁻², Q₁ and Q₂ are the charges (C), r is the distance between them (m), and ε₀ is the permittivity of free space (8.85 × 10⁻¹² F m⁻¹).
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