Coulomb's Law
Drag two charges and watch the inverse-square force update live, with proper LaTeX formula.
Key Notes
Force between two point charges in vacuum is F = kq₁q₂/r² where k = 1/(4πε₀) = 8.99 × 10⁹ N·m²/C².
Force is along the line joining the charges. Like charges repel, unlike charges attract.
Coulomb force obeys Newton's third law — charges experience equal and opposite forces.
In a medium of relative permittivity εᵣ, force becomes 1/εᵣ times the vacuum value.
Inverse-square dependence: doubling distance reduces force by factor 4.
Formulas
Coulomb's Law
Magnitude of force; k ≈ 9×10⁹ N·m²/C².
Vector form
Force on q₂ due to q₁; r̂ is unit vector from 1 to 2.
In medium
Reduced by relative permittivity.
Important Points
ε₀ = 8.854 × 10⁻¹² C²/(N·m²); k = 1/(4πε₀).
Coulomb's law applies only to STATIC point charges. Moving charges also produce magnetic fields.
Charge is quantised: q = ne, with e = 1.6 × 10⁻¹⁹ C; conserved in any closed system.
Superposition holds: F⃗_net = ΣF⃗ᵢ on a test charge.
Coulomb's Law notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 12 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.