Chapter 21: Electric Charge and Electric Field

Coulomb's law provides the quantitative foundation for calculating electrostatic forces between point charges, incorporating the inverse square distance relationship and vector superposition for multiple charge systems. The electric field concept emerges as a powerful tool for describing how charges create force fields in surrounding space, with field strength defined as force per unit test charge and visualized through field line representations that indicate direction and relative magnitude. Students learn to calculate electric fields from various charge configurations, including point charges, charge distributions with linear, surface, and volume densities, and continuous charge arrangements like rings, disks, and infinite planes using integration techniques. Electric dipoles receive special attention as fundamental charge arrangements, with detailed analysis of dipole moments, torque effects in external fields, and potential energy relationships that determine stable and unstable orientations. The chapter demonstrates how electric field calculations rely on vector superposition principles, allowing complex field patterns to be determined by summing contributions from individual charge elements. Field line visualization techniques help students understand field patterns, with lines originating from positive charges, terminating on negative charges, and maintaining density proportional to field strength while never intersecting.