Coulomb's Law (magnitude) (F = k |q1 q2| / r²)

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F = k |q1 q2| / r²

What each symbol means

SymbolWhat it stands for
FElectrostatic force magnitude between two point charges (N)
rDistance between charges (m)
q_1,q_2Point charges (C); use signs separately for direction
\varepsilon_0Permittivity of free space (F/m)

When to use this

Point charges in vacuum (or use ε for medium via k→k/εr). Static charges. Superposition holds for multiple pairs.