Electrical comprehension swaps gears and pulleys for cells, bulbs, switches and resistors. You're shown a circuit diagram and asked to trace current through it: which bulbs light when this switch closes, what happens to the others when one filament blows, does moving a resistor from series to parallel make the bulbs brighter or dimmer, what current flows for a given voltage and resistance? The physics is Ohm's law and a handful of everyday electrics — fuses, earth wires, electromagnets, motors, transformers — but the skill being tested is the same as any technical-comprehension item: read a static diagram and correctly reason through what happens when it's live.
Why airlines test it
This measures the electrical half of technical comprehension — a feel for how current, voltage and resistance behave in a circuit, and where the classic misconceptions lie (current 'getting used up' as it passes through a component, a battery supplying a fixed current regardless of load, parallel branches always sharing equally). An aircraft's electrical system is layered with exactly this kind of series/parallel logic multiplied across buses and generators, and airlines want pilots who can reason through a circuit rather than just recognise one from a diagram.
In the cockpit
Every aircraft electrical system is buses, generators, batteries and load-shedding logic — a real circuit diagram you're expected to reason through under pressure, not just memorise. When a generator or bus fails, the question is never abstract: which equipment sat on that bus, what's still powered from elsewhere, and what needs shedding to keep the essentials alive. That's the same reasoning as an electrical-comprehension question — trace the circuit, work out what's still live, and know why.
For example: the aircraft loses its left generator in cruise. The left bus now depends on the battery or a cross-tie from the right generator, and a handful of non-essential loads — perhaps a galley feed or a windscreen heat element — auto-shed to protect the remaining capacity. You need to reason, in seconds, which instruments and systems are still fed from the surviving source and which ones just went dark — exactly the same skill as tracing which bulb dims when a switch opens in a parallel circuit.
How to practise
Practise with Electrical Comprehension, which drills circuits and switches, series versus parallel behaviour, Ohm's law and power, and practical electrics and magnetism through timed multiple-choice items with circuit diagrams. Before answering, trace the diagram deliberately — label what's in series and what's in parallel, then ask what a switch or a blown bulb does to current in every branch, not just the one you're looking at. Only commit once you've actually traced the circuit rather than pattern-matched the diagram.