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

Electrical Comprehension syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Electrical Comprehension in RAF Airman/Airwoman Selection Test (AST), not a summary of it.

1. 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. 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. 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

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

24 of 50 cards from the Electrical Comprehension deck — real questions with worked 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. $$V_{1} = V_{2} = V_{3} = V_{\text{supply}}$$

21. 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: $$I_{\text{total}} = I_{1} + I_{2} + I_{3} + \dots$$

22. 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.

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

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

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

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

See more Electrical Comprehension flashcards →

Planning Electrical Comprehension for RAF Airman/Airwoman Selection Test (AST)

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