Basic Electricity
Electricity items on the General test are overwhelmingly Ohm's law, series and parallel rules, batteries, and the practical habits of wiring and bonding. Get the two circuit rules cold and most questions answer themselves.
Series: the current is the same everywhere; voltages divide; resistances add. Parallel: the voltage is the same across every branch; currents add; total resistance is always less than the smallest branch. For two resistors, R = (R1 × R2) ÷ (R1 + R2). Power is P = I × E, and in a resistive circuit electrical energy always appears as heat.
Know that a voltmeter goes across the load (parallel) and an ammeter goes in the circuit (series); never check resistance or continuity on a live circuit. Lead-acid cells are about 2.1 V, so a 24-volt battery has 12 cells; nickel-cadmium cells are about 1.2 V. Alternators generate AC that is rectified; generators generate DC and need a regulator and a cutout.
Traps. Questions love the parallel-resistance rule, and the answer must be smaller than the smallest resistor. Watch for the difference between electron flow (negative to positive) and conventional current, the reason for bonding (equalizing static potential before fueling), and the fact that a fuse or circuit breaker protects the wire, not the component.
Worked example. Two 12-ohm resistors in parallel across 24 V. R = (12 × 12) ÷ 24 = 6 ohms. Total current I = 24 ÷ 6 = 4 A, so 2 A flows in each branch, and P = 24 × 4 = 96 W.