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RAF Airman/Airwoman Selection Test (AST) Electrical Comprehension Syllabus

The Electrical Comprehension syllabus for RAF Airman/Airwoman Selection Test (AST) in full: 3 chapters, 13 topics and 6 sub-topics, every one listed below, plus 50 Electrical Comprehension flashcards with answers.

3Chapters
13Topics
6Sub-topics
50Flashcards

Electrical Comprehension syllabus: all 3 chapters

Expand any chapter to see its topics and sub-topics.

  1. Fundamentals of Electricity

     4 topics
    • Voltage, current and resistance
      • Ohm's law and its application
    • Conductors and insulators
    • Direct current and alternating current
    • Power, energy and units (watts, amps, volts)

  2. Circuit Analysis

     4 topics
    • Series circuits
      • Adding resistances in series
      • Effect of a broken component
    • Parallel circuits
      • Current paths in parallel branches
    • Reading basic circuit diagrams
      • Recognising standard component symbols
    • Switches and how they control current flow

  3. Components and Practical Concepts

     5 topics
    • Batteries, cells and power sources
    • Resistors, capacitors and diodes
      • What each component does
    • Fuses, earthing and safety devices
    • Bulbs and load behaviour in circuits
    • Magnetism and electromagnetism basics

RAF Airman/Airwoman Selection Test (AST) Electrical Comprehension flashcards — 50 questions with answers

  1. Define electric current and state its SI unit.

    Electric current is the rate of flow of electric charge through a conductor. Its SI unit is the ampere ($\text{A}$), where $1\,\text{A} = 1\,\text{C/s}$ (one coulomb per second).

  2. Define voltage (potential difference) and state its unit.

    Voltage is the potential difference, or the energy per unit charge, that drives current around a circuit (the "push"). Its unit is the volt ($\text{V}$), where $1\,\text{V} = 1\,\text{J/C}$.

  3. Define electrical resistance and state its unit.

    Resistance is the opposition a material offers to the flow of current. Its unit is the ohm ($\Omega$), where $1\,\Omega = 1\,\text{V/A}$.

  4. State Ohm's law as a formula and in words.

    $$V = I \times R$$ The voltage across a component equals the current through it multiplied by its resistance (current is proportional to voltage for a fixed resistance).

  5. Rearrange Ohm's law to find current and to find resistance.

    $$I = \frac{V}{R} \qquad R = \frac{V}{I}$$

  6. What is the difference between a conductor and an insulator?

    A conductor has many free electrons and allows current to flow easily (low resistance). An insulator has very few free charge carriers and strongly opposes current flow (very high resistance).

  7. Give two common examples each of conductors and insulators.

    Conductors: copper, silver, gold, aluminium. Insulators: rubber, plastic, glass, dry wood, air.

  8. Why is copper the most common material for electrical wiring?

    Copper is an excellent conductor (very low resistance), is relatively cheap, ductile so it can be drawn into wires, and resists corrosion.

  9. What is the difference between direct current (DC) and alternating current (AC)?

    In direct current the charge flows in one constant direction (e.g. from a battery). In alternating current the direction of flow reverses periodically (e.g. from the mains supply).

  10. State the frequency and nominal voltage of the UK mains AC supply.

    The UK mains supplies alternating current at $50\,\text{Hz}$ and a nominal voltage of $230\,\text{V}$.

  11. Give one practical advantage of AC over DC for power distribution.

    AC voltage can easily be stepped up or down using transformers, allowing efficient high-voltage transmission over long distances with low energy losses.

  12. Define electrical power and give the basic formula.

    Power is the rate at which electrical energy is transferred or work is done. $$P = V \times I$$ Its unit is the watt ($\text{W}$), where $1\,\text{W} = 1\,\text{J/s}$.

  13. Write two alternative formulas for electrical power using resistance.

    $$P = I^{2} R \qquad P = \frac{V^{2}}{R}$$

  14. State the formula linking electrical energy, power and time.

    $$E = P \times t$$ Energy equals power multiplied by time. The SI unit is the joule ($\text{J}$); the commercial unit is the kilowatt-hour ($\text{kWh}$).

  15. Match each quantity to its unit: power, current, voltage, resistance, energy.

    Power $\to$ watt ($\text{W}$); current $\to$ ampere ($\text{A}$); voltage $\to$ volt ($\text{V}$); resistance $\to$ ohm ($\Omega$); energy $\to$ joule ($\text{J}$).

  16. Define electric charge and state its unit.

    Charge is a fundamental property of matter responsible for electrical effects, carried by electrons and protons. Its unit is the coulomb ($\text{C}$), and $Q = I \times t$.

  17. In a series circuit, how does the current behave at every point?

    The current is the same at every point in a series circuit, because there is only one path for the charge to flow through. $$I_{1} = I_{2} = I_{3}$$

  18. How is total resistance calculated for resistors in series?

    The resistances add together: $$R_{\text{total}} = R_{1} + R_{2} + R_{3} + \dots$$

  19. How is the supply voltage shared in a series circuit?

    The supply voltage is divided across the components, so the sum of the voltage drops equals the supply voltage: $$V_{\text{supply}} = V_{1} + V_{2} + V_{3} + \dots$$

  20. In a parallel circuit, how does the voltage across each branch compare?

    The voltage across each parallel branch is the same and equals the supply voltage. $$V_{1} = V_{2} = V_{3} = V_{\text{supply}}$$

Show the other 30 Electrical Comprehension flashcards

  1. How is total current related to branch currents in a parallel circuit?

    The total current from the source equals the sum of the currents in the individual branches: $$I_{\text{total}} = I_{1} + I_{2} + I_{3} + \dots$$

  2. State the formula for total resistance of resistors in parallel.

    $$\frac{1}{R_{\text{total}}} = \frac{1}{R_{1}} + \frac{1}{R_{2}} + \frac{1}{R_{3}} + \dots$$ The total resistance is always less than the smallest individual resistance.

  3. For two resistors in parallel, give the simplified product-over-sum formula.

    $$R_{\text{total}} = \frac{R_{1} \times R_{2}}{R_{1} + R_{2}}$$

  4. Calculate the total resistance of two $6\,\Omega$ resistors connected in parallel.

    $$R = \frac{6 \times 6}{6 + 6} = \frac{36}{12} = 3\,\Omega$$

  5. Why do festive lights wired in parallel keep working if one bulb fails, but series ones do not?

    In parallel each bulb has its own path, so a break in one branch does not interrupt the others. In series there is a single path, so one failed bulb breaks the whole circuit.

  6. What does the standard circuit symbol of a long thin line and a short thick line represent?

    A single cell. The longer thin line is the positive ($+$) terminal and the shorter thick line is the negative ($-$) terminal.

  7. How is a resistor drawn in a UK-style circuit diagram?

    A resistor is shown as a plain rectangular box (in older diagrams, a zig-zag line).

  8. What components do an empty circle and a circle with a cross inside usually represent on a circuit diagram?

    A plain circle is commonly a lamp/indicator or meter; a circle with a cross inside it represents a lamp (bulb). A circle with 'A' is an ammeter and one with 'V' is a voltmeter.

  9. How should an ammeter and a voltmeter each be connected in a circuit?

    An ammeter is connected in series (to measure the current flowing through). A voltmeter is connected in parallel across a component (to measure the potential difference across it).

  10. What is the function of a switch in a circuit?

    A switch makes or breaks the circuit, controlling whether current can flow. Closed (on) completes the path so current flows; open (off) breaks the path so no current flows.

  11. What is the difference between an open switch and a closed switch?

    An open switch leaves a gap in the circuit so no current flows. A closed switch completes the conducting path, allowing current to flow.

  12. To switch a single lamp on or off independently while others stay on, how must the switch be wired?

    It must be wired in series with that lamp only (typically on its own parallel branch), so opening it breaks only that branch.

  13. What is the difference between a cell and a battery?

    A cell is a single electrochemical unit that produces a voltage. A battery is two or more cells connected together (usually in series) to give a larger voltage or capacity.

  14. What happens to the total voltage when identical cells are connected in series?

    The voltages add up. For example, three $1.5\,\text{V}$ cells in series give $$3 \times 1.5 = 4.5\,\text{V}$$

  15. What happens when identical cells are connected in parallel?

    The voltage stays the same as a single cell, but the total capacity (and the current the battery can supply / its life) increases.

  16. What is the difference between a primary cell and a secondary cell?

    A primary cell is single-use and cannot be recharged (e.g. an alkaline AA). A secondary cell is rechargeable and can be reused many times (e.g. a lithium-ion or lead-acid battery).

  17. What is the function of a resistor in a circuit?

    A resistor opposes/limits the flow of current and is used to control current and divide voltage. It converts some electrical energy into heat.

  18. What is the function of a capacitor?

    A capacitor stores electrical charge (and energy) in an electric field between two plates, and can release it. It blocks DC once charged but passes AC, and smooths or filters signals.

  19. What is the function of a diode?

    A diode allows current to flow in one direction only (forward), blocking it in the reverse direction. It is used for rectification (converting AC to DC) and to protect circuits.

  20. What does an LED do and what does the abbreviation stand for?

    An LED (Light Emitting Diode) is a diode that emits light when current flows through it in the forward direction. It conducts in one direction only.

  21. What is the purpose of a fuse in an electrical circuit?

    A fuse is a safety device containing a thin wire that melts and breaks the circuit if the current exceeds a safe value, preventing overheating, fire and equipment damage.

  22. How should a fuse be connected and why does it protect the circuit?

    A fuse is connected in series, normally in the live wire. Because it carries the full circuit current, an excessive current melts its element and breaks the whole circuit.

  23. What is the purpose of earthing (grounding) an appliance?

    Earthing provides a low-resistance path for fault current to flow safely to ground. If a live wire touches a metal casing, the large current blows the fuse instead of leaving the case live, protecting the user from electric shock.

  24. State the standard colours of the live, neutral and earth wires in a UK three-pin plug.

    Live = brown; Neutral = blue; Earth = green-and-yellow stripes.

  25. What does an RCD do and how does it differ from a fuse?

    A Residual Current Device detects a small imbalance between live and neutral currents (indicating leakage to earth) and cuts the supply very quickly to prevent shock. A fuse only responds to excessive overall current, and more slowly.

  26. How does the resistance of a typical filament bulb change as it heats up?

    As the filament heats up, its resistance increases. A hot filament therefore has a higher resistance than a cold one, so the current is largest at the instant of switch-on.

  27. What does adding more identical bulbs in series do to their brightness?

    Adding more bulbs in series increases total resistance, reducing the current, so each bulb becomes dimmer.

  28. What happens to the current drawn from the supply as more bulbs are added in parallel?

    Each added parallel bulb provides an extra path, reducing total resistance, so the total current drawn from the supply increases (while each bulb stays at the same brightness).

  29. What is the basic rule of magnetic poles?

    Like poles repel and unlike poles attract. A magnet always has both a north and a south pole, and field lines run from north to south outside the magnet.

  30. What is electromagnetism, and how can the strength of an electromagnet be increased?

    Electromagnetism is the magnetic effect produced when current flows through a conductor; a coil of wire (solenoid) carrying current acts as a magnet. Its strength is increased by increasing the current, adding more turns of wire, or inserting a soft-iron core.

RAF Airman/Airwoman Selection Test (AST) Electrical Comprehension FAQ

What is in the RAF Airman/Airwoman Selection Test (AST) Electrical Comprehension syllabus?

RAF Airman/Airwoman Selection Test (AST) Electrical Comprehension is split into 3 chapters: Fundamentals of Electricity, Circuit Analysis and Components and Practical Concepts. Together they contain 13 topics and 6 sub-topics.

How many chapters are in RAF Airman/Airwoman Selection Test (AST) Electrical Comprehension?

3 chapters, containing 13 topics and 6 sub-topics. The largest chapter is Components and Practical Concepts, with 5 topics.

Are there flashcards for RAF Airman/Airwoman Selection Test (AST) Electrical Comprehension?

Yes — a 50-card Electrical Comprehension deck, printed in full in the flashcards section of this page and available in the Examius app with spaced repetition. The free plan covers one exam of your choice, including its flashcards; Examius Pro, a one-time purchase, unlocks every other exam and deck.