Coulomb's Law

Coulomb's Law

Coulomb's Law

Coulomb's law describes the electric force between two point charges.

The magnitude is:

**F = k|q₁q₂|/r²**

where:

0 = electrostatic force;

0, 1 = charges;

0 = separation;

`k ≈ 8.99 × 10⁹ N m² C⁻²` in vacuum.

Meaning

Greater charges → stronger force.

Greater distance → weaker force.

Because:

**F ∝ 1r²**

doubling separation reduces force to one quarter.

Direction

Like charges repel.

Unlike charges attract.

The force acts along the line joining the two charges.

Worked Example

`q₁ = 2 μC`

`q₂ = 3 μC`

`r = 0.20 m`

Convert:

`2 μC = 2×10⁻⁶ C`

`3 μC = 3×10⁻⁶ C`

Then:

`F = (8.99×10⁹)(2×10⁻⁶)3×10⁻⁶0.20²`

`F ≈ 1.35 N`

Coulomb's Law — Advanced