Alternating Current

Chapter Overview

Alternating Current (AC) is a central concept in power transmission and electrical engineering. This chapter begins by describing how alternating voltage and current vary sinusoidally over time, defining peak values, instantaneous values, root-mean-square (RMS) values, and mean values. Students learn vector representations (phasor diagrams) of alternating quantities to visualize phase differences, identifying phase lead and phase lag conditions across different circuit components.

The chapter systematically investigates AC circuit behavior through individual passive components: resistors (where voltage and current are in phase), inductors (where voltage leads current by 90° with zero average power dissipation), and capacitors (where current leads voltage by 90°). Inductive reactance X_L = 2πfL and capacitive reactance X_C = 1/(2πfC) are formulated, alongside the function of a choke coil in controlling AC with minimal energy loss. These principles converge in the calculation of total impedance Z in series RC, RL, and RLC circuits.

A major focus is devoted to resonant circuits. Students analyze resonance frequency, impedance minimization, and current maximization in series RLC circuits, contrasting them with parallel RLC rejector circuits. The chapter further explores electromagnetic induction mechanisms, specifically self induction and mutual induction, and explains AC-to-DC conversion through half-wave and full-wave rectification. This foundational coverage enables intermediate students to master board derivations, phasor sketches, and numerical calculations.