Alternating Current

Sinusoidal AC voltage generation, root-mean-square values, and complex RLC circuit impedance.

General idea of the topic

Alternating current describes circuits where voltage and current vary periodically in time, introducing phase as the essential variable that determines how power splits between active and reactive components.

Unlike direct current, frequency modifies the behavior of every element: capacitive and inductive reactances control the circuit response and impedance unifies resistance and reactance in a single phasor formalism.

What you will truly understand

  • Difference between peak value, RMS and phase.
  • Effect of capacitive and inductive reactance with frequency.
  • Solving RLC circuits by impedance.
  • Resonance, selectivity and quality factor.

Recommended learning route

  1. AC quantities.
  2. Capacitive and inductive reactance.
  3. RLC circuits.
  4. Electrical resonance.

Physical criterion you must acquire

Interpret AC as a phenomenon of energy and phase: it is not enough to solve equations; you must justify which quantity is RMS, which component is reactive and in which domain the model operates.

Connection with real problems

Appears in electrical grids, motors, filters, audio, telecommunications and power conversion.

Final goal of the topic

Solve alternating-current problems with full traceability of frequency, phase, power and impedance.

Topics in this section

  • AC Quantities

    Introduces amplitude, RMS, frequency, period, and phase to interpret AC signals and power.

  • Reactance

    Capacitive and inductive reactance opposing alternating current flow in circuit elements.

  • RLC Circuits

    Analyzes impedance, phase, and power in AC series RLC circuits. Theory, formulas, worked examples and interactive graphs.

  • Electrical Resonance

    Relates resonant frequency, quality factor, and bandwidth to interpret selectivity in RLC circuits.