Electrostatics / Static Electricity

Chapter Overview

Electrostatics (Static Electricity) is a fundamental branch of electromagnetism that investigates electrical charges at rest and their electrostatic interactions. The chapter explores electric potential difference-defined as work done per unit positive test charge in moving between two points against an electrostatic field-and absolute electric potential. It develops the quantitative derivation for the electric potential energy of a two-point-charge system, linking field intensity with potential gradient through the relation E = -ΔV / Δr.

A major focus is dedicated to charge storage devices: capacitors. The chapter begins with isolated spherical conductors and progresses to parallel plate capacitors, evaluating how plate surface area, separation distance, and dielectric medium (relative permittivity) dictate capacitance through C = ε₀ ε_r A / d. It rigorously derives equivalent capacitance formulas for capacitors connected in series (1/C_eq = 1/C_1 + 1/C_2 + ...) and parallel (C_eq = C_1 + C_2 + ...), as well as the electric potential energy stored in an electrostatic field: U = ½CV².

The practical dynamics of capacitive circuits are explored through RC charging and discharging processes. Students study exponential growth and decay curves, defining the role of the capacitive time constant τ = RC (the time required for a capacitor to charge to 63.2% or discharge to 36.8% of its maximum value). The chapter concludes with real-world applications of capacitors in electric fans, motor starters, refrigeration compressors, camera flashguns, and power supply rectification filter circuits.