Electric Charge & Coulomb’s Law — A/L Physics

Electric Charge (Q) A fundamental property of matter that causes it to experience a force in an electric field. Charge is quantized, existing in integer multiples of the elementary charge e = 1.602 × 10⁻¹9 C . Protons carry positive charge, electrons carry negative charge. In nature, charge is conserved — it cannot be created or destroyed, only transferred. Example: Rubbing a plastic ruler with fur transfers electrons, giving the ruler a net negative charge.

Coulomb’s Law The electrostatic force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. Mathematically, F = k (q₁ q₂)/(r²) , where k = 8.99 × 10⁹ N·m²/C² . The force is attractive for opposite charges and repulsive for like charges. Example: Two identical charges repel each other; the force quadruples if the distance is halved.