15.4 Coulomb's Law
Charges can repel and attract each other with a force called electrostatic force. Charles Coulomb, in 1785, provided an experimental law to explain the nature and magnitude of electrostatic force between charges.
lightbulbCoulomb's law states that the magnitude of the electrostatic force between two point charges is directly proportional to the product of the magnitudes of these charges and inversely proportional to the square of the distance between them.
Consider two charges q₁ and q₂ separated by distance r. Mathematically:
F ∝ q₁ q₂
F ∝ 1 / r²
F = k q₁ q₂ / r²
where k is a constant of proportionality. In vacuum or air, k is approximately 9 × 10⁹ N m² C⁻². Coulomb's law is applicable primarily to point charges whose sizes are negligible compared to the distance separating them.