Electrical Fundamentals: DC Circuits, Magnetism and AC Basics
Core concepts
Understand Ohm's law, series and parallel circuits, Kirchhoff's laws, and power dissipation. Know how to calculate equivalent resistance and how current divides in parallel branches. Understand the magnetic effect of current, electromagnetism, and the operation of relays, solenoids and transformers.
AC and aircraft supply
Know the difference between DC and AC, the meaning of frequency and phase, and why aircraft use 400 Hz AC (smaller, lighter transformers and motors). Understand the principle of the generator and the alternator, and the role of rectifiers and inverters. Know the basics of batteries (lead-acid versus nickel-cadmium) and their care, including thermal runaway risk in NiCd.
Wiring and protection
Understand circuit protection (fuses, circuit breakers), wire sizing, voltage drop, and the importance of correct bonding and shielding to control electromagnetic interference. Know the meaning of a bus bar and how essential and non-essential buses are separated.
Traps
- Mixing series and parallel rules; resistance in parallel is always less than the smallest branch.
- Forgetting that voltage is common across parallel branches, while current is common in series.
- Assuming a larger fuse is safer; it may fail to protect the wire.
Worked example
Two resistors, 6 Ω and 3 Ω, in parallel across 12 V. Equivalent resistance = (6×3)/(6+3) = 2 Ω. Total current = 12/2 = 6 A; branch currents are 2 A and 4 A. Check: 2+4 = 6 A.