Coulomb's constant and permittivity (k = 1/(4πε₀))

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k = 1/(4πε₀)

What each symbol means

SymbolWhat it stands for
kCoulomb constant ≈ 8.99×10⁹ N·m²/C²
\varepsilon_0Vacuum permittivity ≈ 8.85×10⁻¹² F/m

When to use this

k and \varepsilon_0 are equivalent constants in SI vacuum electrostatics.