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EASA Part-66 Module 3 Cats A · B1 · B2 · B2L · B3

Electrical Fundamentals EASA Part-66 — Module 3 Practice Questions

Module 3 covers the electrical theory that underpins every system on a modern aircraft — from electron flow and Ohm's Law through DC and AC circuits, magnetism, transformers and motors. Below: the 18 sub-sections, exam format for each licence category, and seven sample questions in exam style.

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Every question comes with a worked, EASA-grounded explanation — understand why, don't just memorise.
1 242
Questions in bank
5
Syllabus sections
65 min
Exam time (B1/B2)
75 %
EASA pass mark

Syllabus at a glance

Full Module 3 syllabus
Section 3.1-3.4
Electrical Fundamentals
  • Electron theory: atoms, ions, conductors & insulators
  • Static electricity, Coulomb's Law & conduction in matter
  • Voltage, current, resistance & EMF terminology
  • Generation of electricity: light, heat, friction, pressure & chemical
Section 3.5-3.8
DC Circuits & Power
  • Primary & secondary cells, lead-acid & nickel-cadmium batteries
  • Ohm's Law, Kirchhoff's voltage & current laws
  • Resistors in series & parallel, colour code, Wheatstone Bridge
  • Power, work & energy — calculations and dissipation
Section 3.9-3.11
Capacitance, Magnetism & Inductance
  • Capacitor types, charge/discharge curves & time constants
  • Properties of magnets, flux density, permeability & hysteresis
  • Faraday's & Lenz's Laws, self & mutual inductance
  • Back EMF and saturation in inductive components
Section 3.12-3.14
DC Machines & AC Theory
  • DC generator and motor construction, series/shunt/compound types
  • Sinusoidal waveforms: phase, period, frequency, RMS & peak values
  • Single and three-phase principles
  • Impedance, phase angle, power factor in R, L & C circuits
Section 3.15-3.18
Transformers, Filters & AC Machines
  • Transformer turns ratio, losses, efficiency & auto-transformers
  • Low pass, high pass, band pass and band stop filters
  • Revolving armature & revolving field AC generators
  • Synchronous and induction motors, methods of speed control

Three classic exam-day traps

Electron flow vs conventional current

Electron flow is negative-to-positive; conventional current is positive-to-negative. Many candidates use the right-hand rule on a left-hand-rule question, or vice versa, and pick a plausible-looking distractor.

Series vs parallel resistance

Series resistors add directly; parallel resistors combine as 1/RT = 1/R1 + 1/R2. Under pressure candidates invert one and not the other, producing an answer that's off by an order of magnitude.

Peak, RMS and average AC values

RMS = peak / √2 for a sine wave, average = peak × 0.637. The three values get mixed up — and the question often quotes peak-to-peak, which is double the peak.

What Module 3 covers — in plain English

Module 3 of the EASA Part-66 syllabus is the electrical theory foundation every licensed aircraft maintenance engineer builds on for the rest of their career. It runs from the structure of the atom all the way through DC and AC circuit analysis, magnetism, transformers and motor theory — eighteen sub-sections in total. Almost every later module touches it: Module 4 (Electronic Fundamentals) assumes you already understand voltage, current and resistance; Module 7 (Maintenance Practices) uses Ohm's Law on every wiring calculation; and the airframe modules constantly refer back to electrical generation, distribution and motor control. Examiners know this is foundational material, so the questions are pitched as applied calculations as much as recall — expect to convert units, manipulate formulas and identify the correct law to invoke before you can pick an answer.

The exam itself is one of the longer Part-66 papers. B1, B2 and B2L candidates sit a 52-question paper in 65 minutes, while B3 candidates sit a 24-question paper in 30 minutes and Category A candidates sit 20 questions in 25 minutes. Time pressure is real — that's roughly 75 seconds per question for the longer papers, and a typical Module 3 question requires a unit conversion or a two-step calculation before you can even identify the right answer. The pass mark is 75 % across all categories, and like every Part-66 paper there is no negative marking — but with the calculator allowed only for arithmetic (not symbolic algebra), candidates who haven't drilled the standard formulas to muscle memory tend to run out of time.

Knowledge depth varies sharply between licence categories. Category A and B3 candidates need only level 1 (basic familiarisation) across the whole syllabus — recognising the principle and naming the components. B1, B2 and B2L candidates need level 2 (general knowledge plus the ability to apply principles) on almost every sub-section except 3.1 (Electron Theory) and 3.4 (Generation of Electricity), which sit at level 1 for everyone. The biggest jump for B1/B2/B2L candidates is in capacitor, inductor and AC-circuit analysis (3.9, 3.11 and 3.14) where numerical calculations are explicitly examinable. B2 avionics candidates also tend to find sub-sections 3.15 (Transformers) and 3.16 (Filters) heavier going than their B1 colleagues, simply because the underlying maths is closer to electronic-circuit analysis than to airframe systems. Full knowledge-level breakdown by sub-section is on our Module 3 syllabus page.

These samples are drawn from our live Module 3 question bank of 1 242 questions. The full timed practice quiz draws 52 questions per attempt (or 20 for Cat A), scored against the official EASA 75 % pass mark, with weak-area tracking across attempts.

7 free sample questions

Click "Reveal answer + explanation" after you've picked.

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Q1 Electrical Terminology

Electromotive force is measured in

  1. A Watts.
  2. B Ohms.
  3. C Volts.
Reveal answer + explanation Hide answer
Correct answer: C — Volts.
EMF is the energy per unit charge supplied by a source, measured in volts (joules per coulomb). Watts measure power (rate of energy transfer) and ohms measure resistance — distinguishing the three SI units is foundational for the rest of Module 3.
Q2 Generation of Electricity

A photozoidal cell produces electricity when subjected to

  1. A light.
  2. B pressure.
  3. C heat.
Reveal answer + explanation Hide answer
Correct answer: A — light.
A photo-electric cell (sometimes spelt phonetically in the exam bank) generates an EMF when light strikes its surface. Pressure produces electricity in piezo-electric devices; heat produces it in thermocouples — Module 3 sub-section 3.4 covers all three.
Q3 Resistance / Resistors

What is the formula for conductance? (R=Resistance)

  1. A R + 1.
  2. B 1/R.
  3. C 1-R.
Reveal answer + explanation Hide answer
Correct answer: B — 1/R.
Conductance (G) is the reciprocal of resistance: G = 1/R. Its SI unit is the siemens (S), formerly the mho. Conductance is useful when combining parallel resistors because it adds directly rather than requiring a reciprocal sum.
Q4 Power

A 10 V battery supplies a resistive load of 10 ohms for 1 minute. What is the power supplied?

  1. A 100 W.
  2. B 10 VA.
  3. C 10 W.
Reveal answer + explanation Hide answer
Correct answer: C — 10 W.
P = V² / R = 10² / 10 = 10 W. The one-minute duration is a distractor — power is the instantaneous rate of energy transfer and is independent of how long the load draws current. Multiply by 60 s and you get energy in joules, not power.
Q5 Inductance / Mutual Induction

When two coils are linked by a common flux, a voltage can be induced in one by a changing current in the other. This process is known as

  1. A self induction.
  2. B the magnetic effect.
  3. C mutual induction.
Reveal answer + explanation Hide answer
Correct answer: C — mutual induction.
Mutual induction is the basis of transformer action — a changing current in the primary creates a changing flux that induces an EMF in the secondary. Self-induction is the back-EMF a coil induces in itself when its own current changes (Lenz's Law).
Q6 AC Theory · Period & Frequency

If a motor is spinning at 50 cycles per second, how long is 1 cycle of the output?

  1. A 50 seconds.
  2. B 0.83 seconds.
  3. C 0.02 seconds.
Reveal answer + explanation Hide answer
Correct answer: C — 0.02 seconds.
Period T is the reciprocal of frequency f: T = 1/f = 1/50 = 0.02 s (20 ms). The 0.83 s distractor is 50/60 — a unit-confusion trap for candidates who think in minutes. 50 Hz is the European mains frequency; aircraft AC busses run at 400 Hz.
Q7 Transformers

How many turns does the secondary winding of a 2:1 step-up transformer have?

  1. A Less than primary.
  2. B More than primary.
  3. C Less turns but with thicker wire.
Reveal answer + explanation Hide answer
Correct answer: B — More than primary.
In a step-up transformer the secondary voltage is greater than the primary, so the secondary must have more turns than the primary (Vs/Vp = Ns/Np). Step-down transformers reverse this. The ratio 2:1 here refers to voltage, not turns direction.
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Module 3 — frequently asked questions

How many questions are in the EASA Part-66 Module 3 exam?
The Category A Module 3 exam has 20 multiple-choice questions, while the Category B1 (and B2/B2L) exam has 52 multiple-choice questions. The counts are not the same — the B1/B2 paper is more than twice as long because those categories are examined to a deeper knowledge level. Each question has three answer options with one correct answer.
What is the pass mark for EASA Part-66 Module 3?
The pass mark for Module 3 is 75%, the same as every EASA Part-66 module. There is no negative marking, so an unanswered or wrong question simply scores zero rather than deducting marks — it is always worth attempting every question. Because Module 3 mixes recall with applied calculations, budget your time so you never leave a solvable question blank.
How long is the Module 3 exam?
Category A candidates have 25 minutes for the 20-question paper, and B1/B2/B2L candidates have 65 minutes for the 52-question paper. That works out to roughly 75 seconds per question — tight for a module where many questions require a unit conversion or a two-step calculation before you can pick an answer. Drilling the standard formulas to muscle memory is the main defence against running out of time.
Which EASA licence categories require Module 3?
Module 3 is required across Categories A, B1, B2, B2L and B3 — it is one of the foundational modules that applies to every licence path. The depth of knowledge differs by category: A and B3 are examined at basic familiarisation level, while B1, B2 and B2L are examined at the higher apply-the-principles level, especially on capacitor, inductor and AC-circuit analysis. You can see the full knowledge-level breakdown by sub-section on our Module 3 syllabus page.
What does Module 3 cover, and what do students find hardest?
Module 3 (Electrical Fundamentals) runs from electron theory and static electricity, through DC circuits, Ohm's Law and Kirchhoff's Laws, into capacitance, magnetism and inductance, then DC and AC machines, transformers and filters — eighteen sub-sections in all. The hardest areas tend to be the ones where a small slip changes the answer by an order of magnitude. Candidates routinely confuse electron flow (negative-to-positive) with conventional current (positive-to-negative), and mix up series versus parallel resistance (series resistors add directly, parallel resistors combine as reciprocals). The AC section is another common stumbling block, where peak, RMS (peak divided by sqrt 2) and average values get interchanged, and peak-to-peak (double the peak) slips into the wrong slot.
How should I revise for Module 3?
Treat Module 3 as an applied-maths paper, not a memorisation exercise: drill Ohm's Law, the power formulas, series/parallel resistance and the AC peak/RMS/average relationships until they are automatic, so you spend exam time reading the question rather than deriving the formula. Practise the classic traps deliberately — electron flow versus conventional current, and inverting one resistor but not the other in a parallel network. Work timed sets so you get used to the roughly 75-seconds-per-question pace, and use our practice questions to expose which sub-sections still cost you time before you sit the real exam.

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Module 3 study resources

Module 3 detailed syllabus
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A · B1 · B2 · B2L · B3 overview

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