Showing content mapped to EASA Part-66. Change authority in the header.
Ohm's law
V = I · R. Voltage (volts) equals current (amps) times resistance (ohms). Power P = V·I = I²·R = V²/R. Use these when sizing bus feeders and calculating heat dissipation in resistors.
Series vs parallel
In series, current is the same through all components and voltages add. Total resistance: R = R1 + R2 + … In parallel, voltage is the same across each branch and currents add. Total resistance: 1/R = 1/R1 + 1/R2 + …
Capacitance & inductance
A capacitor stores energy in an electric field (farads). It blocks DC in steady state and passes AC. An inductor stores energy in a magnetic field (henries) — it passes DC and opposes changes in current. Reactance: Xc = 1/(2πfC), XL = 2πfL.
AC theory
AC alternates polarity sinusoidally. Peak, RMS and average values matter: Vrms = 0.707·Vpeak. Aircraft primary AC bus is often 115 V 400 Hz 3-phase — the higher frequency lets transformers and motors be smaller and lighter.
DC generators & alternators
A DC generator uses a commutator to rectify the induced AC. An alternator produces AC that is then rectified for the DC bus. Voltage regulation is essential — the aircraft's Generator Control Unit (GCU) maintains system voltage as load and rpm change.