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Module 3 Electrical fundamentals: 50 practice questions

Real EASA paper: Category A 20 Q / 25 min · B1.1 52 Q / 65 min · B1.2 52 Q / 65 min · B1.3 52 Q / 65 min · B2 52 Q / 65 min · B2L 52 Q / 65 min · B3 24 Q / 30 min. Three options, 75% to pass. Answer key on the last page. From part66exam.com · independent study aid, not an official exam or a past paper.

  1. 1. A single-phase supply is taken from

    1. A. all three phases together
    2. B. a DC generator with slip rings
    3. C. one phase winding and a neutral or return

  2. 2. The Earth's magnetic north pole behaves magnetically as

    1. A. a north pole, since it repels the north pole of a compass
    2. B. a south pole, since it attracts the north pole of a compass
    3. C. a neutral point with no polarity

  3. 3. In a purely resistive AC circuit, the voltage and current are

    1. A. in phase
    2. B. 90° out of phase with current leading
    3. C. 90° out of phase with current lagging

  4. 4. A supply has significant internal resistance. When the load resistance is reduced, the terminal voltage

    1. A. falls, because more current causes a larger internal drop
    2. B. rises, because the load then takes less of the voltage
    3. C. stays equal to the EMF of the supply

  5. 5. The cut-off frequency of a filter is usually defined as the frequency at which the output

    1. A. has fallen to zero volts
    2. B. exactly equals the input
    3. C. is 70.7 % of maximum (−3 dB)

  6. 6. The electrons in the outermost shell of an atom are called:

    1. A. valence electrons
    2. B. free electrons
    3. C. bound inner-shell electrons

  7. 7. In an ideal inductor on AC, the average power consumed is

    1. A. I² × X_L watts
    2. B. zero watts
    3. C. V × I watts

  8. 8. A current of 400 mA flows through a sensor circuit. Expressed in amperes, this current is

    1. A. 0.4 A
    2. B. 4 A
    3. C. 400000 A

  9. 9. A voltage-dependent resistor (VDR or varistor) is used to

    1. A. protect circuits against voltage spikes
    2. B. provide a fixed reference voltage
    3. C. measure temperature

  10. 10. A conductor 0.5 m long moves at 15 m/s through a 0.7 T field, its motion making an angle of 60° with the lines of flux. What EMF is induced?

    1. A. 2.625 V
    2. B. 5.25 V
    3. C. 4.547 V

  11. 11. One watt is equal to

    1. A. one joule per second
    2. B. one coulomb per second
    3. C. one volt per ampere

  12. 12. Capacitive reactance

    1. A. is independent of frequency
    2. B. increases as frequency increases
    3. C. decreases as frequency increases

  13. 13. What two units are combined in an integrated drive generator (IDG)?

    1. A. a constant speed drive and a generator
    2. B. a starter motor and a DC generator
    3. C. a transformer and a bridge rectifier

  14. 14. Interpoles in a DC generator are used to

    1. A. increase the strength of the main field
    2. B. reduce brush sparking caused by armature reaction
    3. C. act as the main field poles of the machine

  15. 15. A transformer rating plate states the rating in kVA rather than kW because

    1. A. heating depends on current, whatever the pf
    2. B. kVA ratings are always greater than 100 kW
    3. C. transformers only ever supply reactive power

  16. 16. Electrostatic discharge (ESD) is a particular hazard to aircraft electronic equipment because

    1. A. static voltages can destroy sensitive semiconductor devices
    2. B. the discharge current melts the wiring insulation
    3. C. the discharge permanently magnetises the equipment chassis

  17. 17. If one phase of a running three-phase motor is lost, the motor will:

    1. A. usually keep running but overheat with reduced torque
    2. B. immediately reverse its direction of rotation
    3. C. speed up to exactly synchronous speed

  18. 18. The nominal voltage of a single lead-acid cell is about:

    1. A. 1.2 V
    2. B. 2.0 V
    3. C. 3.6 V

  19. 19. An oscilloscope shows a sine wave with a peak value of 160 V. What is its RMS value?

    1. A. 226.24 V
    2. B. 101.92 V
    3. C. 113.12 V

  20. 20. Reversing the current through an electromagnet coil will

    1. A. reverse the polarity of its poles
    2. B. increase its strength
    3. C. destroy the magnetic field

  21. 21. The impedance of a series circuit with R = 3 Ω and X = 4 Ω is:

    1. A. 7 Ω
    2. B. 1 Ω
    3. C. 5 Ω

  22. 22. A meter movement of 0.05 mA full scale and 500 Ω internal resistance is to be used as a voltmeter reading 25 V full scale. What series multiplier resistance is required?

    1. A. 500000 Ω
    2. B. 499500 Ω
    3. C. 500500 Ω

  23. 23. In a T-section low-pass filter, the components are arranged as:

    1. A. two series capacitors with a shunt inductor between them
    2. B. a series inductor with shunt capacitors at each end
    3. C. two series inductors with a shunt capacitor between them

  24. 24. The movement of free electrons through a copper wire occurs because

    1. A. the fixed nuclei vibrate and pass the charge along the lattice
    2. B. valence electrons drift from atom to atom under an applied voltage
    3. C. protons move from atom to atom toward the negative terminal

  25. 25. Inductors of 10 mH, 40 mH and 120 mH are connected in series with no mutual coupling. What is the total inductance?

    1. A. 7.5 mH
    2. B. 56.67 mH
    3. C. 170 mH

  26. 26. Electromotive force (EMF) is best described as:

    1. A. the energy per unit charge supplied by a source
    2. B. the opposition of a conductor to current
    3. C. the rate of flow of charge

  27. 27. A resistor's colour bands decode to the digits 2 and 9 followed by a multiplier of 10 raised to the power 3. What is its resistance?

    1. A. 29000 Ω
    2. B. 92000 Ω
    3. C. 290000 Ω

  28. 28. A solar (photovoltaic) cell converts

    1. A. chemical energy into light energy
    2. B. heat energy into mechanical energy
    3. C. light energy directly into electrical energy

  29. 29. A resistor of 22 Ω is rated at 5 W. What is the maximum current it can carry without exceeding its rating?

    1. A. 0.2273 A
    2. B. 0.4767 A
    3. C. 10.4881 A

  30. 30. When capacitors are connected in series, the total capacitance is

    1. A. less than the smallest individual capacitance
    2. B. the sum of the individual capacitances
    3. C. greater than the largest individual capacitance

  31. 31. A two-phase alternator has

    1. A. two windings displaced by 120°
    2. B. one winding with a centre tap
    3. C. two windings displaced by 90°

  32. 32. A shunt-wound DC motor is characterised by

    1. A. fairly constant speed over a wide load range
    2. B. very high starting torque
    3. C. speed that rises sharply as load is removed

  33. 33. The phase current in each winding of a delta-connected load is 20 A. What is the line current?

    1. A. 20 A
    2. B. 34.64 A
    3. C. 60 A

  34. 34. The force of attraction between two charges is 12 N. If one of the charges is halved and the distance is unchanged, the new force is

    1. A. 6 N
    2. B. 24 N
    3. C. 3 N

  35. 35. The speed of an induction motor rises at no load towards:

    1. A. synchronous speed but never reaches it
    2. B. zero, because no torque is produced
    3. C. twice synchronous speed when unloaded

  36. 36. Hydrogen is released from a battery on charge. Which precaution is correct?

    1. A. Charge only in a closed, unventilated room
    2. B. Seal the vent caps tightly during charging
    3. C. Keep flames and sparks away and ensure good ventilation

  37. 37. The wavelength of an electromagnetic wave is

    1. A. the maximum height of the wave
    2. B. the time taken to complete one cycle
    3. C. the distance travelled in one cycle

  38. 38. Which material is most suitable for a permanent magnet?

    1. A. Alnico alloy
    2. B. Soft iron
    3. C. Copper

  39. 39. Apparent power is measured in

    1. A. watts (W)
    2. B. volt-amperes (VA)
    3. C. volt-amperes reactive (VAR)

  40. 40. A voltage divider of 2 kΩ (top) and 1 kΩ (bottom) is connected across 9 V. The voltage across the bottom resistor is:

    1. A. 3 V
    2. B. 6 V
    3. C. 4.5 V

  41. 41. When an atom gives up one or more of its electrons, it is described as a:

    1. A. negative ion
    2. B. neutral molecule
    3. C. positive ion

  42. 42. The current in an RL circuit rises to what percentage of its final value after one time constant?

    1. A. 63.2 %
    2. B. 100 %
    3. C. 36.8 %

  43. 43. The unit of conductance is the

    1. A. henry
    2. B. siemens
    3. C. ohm

  44. 44. In the resistor colour code, a gold band in the tolerance position indicates

    1. A. ±20 %
    2. B. ±5 %
    3. C. ±10 %

  45. 45. A piezoelectric crystal generates a voltage when it is

    1. A. exposed to light
    2. B. mechanically stressed
    3. C. heated at one end

  46. 46. A 1 kW heater operates for 30 minutes. The energy used is

    1. A. 0.5 kWh
    2. B. 2 kWh
    3. C. 30 kWh

  47. 47. Three capacitors of 2 µF, 8 µF and 25 µF are wired side by side, in parallel. Find their equivalent capacitance.

    1. A. 1.504 µF
    2. B. 35 µF
    3. C. 11.667 µF

  48. 48. In a revolving-field alternator,

    1. A. the armature rotates and the output is taken through slip rings
    2. B. both the field and armature rotate
    3. C. the field rotates and the output is taken from a stationary armature

  49. 49. A 24 V DC motor has an armature resistance of 0.5 Ω. When running, its back EMF is 22 V. What armature current flows?

    1. A. 48 A
    2. B. 4 A
    3. C. 92 A

  50. 50. A transformer works on the principle of

    1. A. self-induction in a single winding only
    2. B. mutual induction between two windings
    3. C. electrostatic induction between plates

Answer key

  1. 1. C — Single-phase loads on aircraft are connected between one phase line and neutral (usually airframe earth), e.g. 115 V from a 115/200 V system.
  2. 2. B — Unlike poles attract. Because the north (seeking) end of a compass is attracted toward the Earth's magnetic north, that region must have south magnetic polarity.
  3. 3. A — A resistor has no energy storage, so current follows the voltage instantly and the phase angle is 0°. Power factor is 1.
  4. 4. A — V_terminal = E − I·r. Reducing the load resistance increases I and hence the internal drop I·r, so less voltage reaches the load.
  5. 5. C — At the −3 dB point the output voltage is 0.707 of the passband value and the output power is half. It defines the edge of the passband.
  6. 6. A — Valence electrons determine how an element bonds and how easily it conducts; conductors have few, loosely held valence electrons.
  7. 7. B — With current 90° out of phase, energy taken during one quarter cycle is returned in the next, so the true power is zero. Real inductors dissipate a little power in their resistance.
  8. 8. A — milli = 10⁻³, so divide by 1 000: 400 mA = 400/1000 = 0.4 A.
  9. 9. A — A varistor has very high resistance at normal voltage but its resistance drops sharply above a threshold, clamping transient spikes and diverting surge current.
  10. 10. C — Only the flux-cutting component counts: e = B·L·v·sin θ = 0.7 × 0.5 × 15 × sin 60° = 4.547 V.
  11. 11. A — 1 W = 1 J/s = 1 V × 1 A. A 100 W lamp converts 100 joules of electrical energy every second.
  12. 12. C — X_C = 1/(2πfC). At higher frequency the capacitor charges and discharges more often per second, so more current flows for the same voltage.
  13. 13. A — The CSD converts variable engine speed into constant generator speed so the output stays at 400 Hz.
  14. 14. B — Interpoles, connected in series with the armature, produce a field that cancels armature reaction in the commutating zone, improving commutation and reducing arcing.
  15. 15. A — Losses depend on current and voltage, not on how much of the power is true power, so the limit is set in volt-amperes.
  16. 16. A — A person can carry several thousand volts of static. Discharging through a sensitive device (MOS gates, thin junctions) can puncture it, so wrist straps and ESD packaging are used.
  17. 17. A — Single-phasing leaves a pulsating field: the motor may continue to run but draws high current and overheats; it will not start from rest.
  18. 18. B — A lead-acid cell gives about 2.0–2.1 V, so a 24 V battery has 12 cells; Ni-Cd cells are 1.2 V.
  19. 19. C — V_rms = 0.707 × V_peak = 0.707 × 160 = 113.12 V.
  20. 20. A — Pole polarity depends on the direction of current around the core. Reversing the current reverses the flux direction and swaps N and S.
  21. 21. C — Z = √(R² + X²) = √(9 + 16) = 5 Ω.
  22. 22. B — Total resistance at full scale = V/I_fs; subtract the meter's own resistance: R_mult = 25/(0.05/1000) − 500 = 499500 Ω.
  23. 23. C — A T low-pass filter has series inductive arms and a shunt capacitive leg; a π filter has shunt capacitors at each end and a series inductor.
  24. 24. B — In a metal, loosely held valence electrons can leave their atoms and drift to neighbouring atoms. An applied potential difference gives this random motion a net direction, which is electric current.
  25. 25. C — Uncoupled series inductors add: 10 + 40 + 120 = 170 mH.
  26. 26. A — EMF (volts) is the work done per coulomb by the source in driving charge around the complete circuit.
  27. 27. A — Value = two significant digits × multiplier = (29) × 10^3 = 29000 Ω.
  28. 28. C — Photons absorbed in a semiconductor junction free electrons and create holes; the junction's internal field separates them, producing a voltage.
  29. 29. B — P = I²R, so I = √(P/R) = √(5/22) = 0.4767 A.
  30. 30. A — Series connection effectively increases plate spacing: 1/C_T = 1/C1 + 1/C2 + … so C_T is less than the smallest capacitor.
  31. 31. C — Two separate windings in quadrature produce two voltages 90° apart.
  32. 32. A — The shunt field is across the supply, so flux is almost constant. Speed drops only slightly with load, suiting fans and pumps.
  33. 33. B — In delta, I_line = √3 × I_phase = 1.732 × 20 = 34.64 A.
  34. 34. A — F = k·Q1·Q2/d². Halving one charge halves the product Q1·Q2, so the force becomes 12/2 = 6 N.
  35. 35. A — With no load, little torque is needed, slip is very small and speed approaches but stays just below synchronous speed.
  36. 36. C — Hydrogen and oxygen form an explosive mixture above about 4 % hydrogen in air. Charging areas must be ventilated, and power switched off before connecting or disconnecting charging leads.
  37. 37. C — λ = v/f. For radio waves v ≈ 3 × 10⁸ m/s, so higher frequencies have shorter wavelengths.
  38. 38. A — Alnico (aluminium-nickel-cobalt) and some ceramic and rare-earth materials have high retentivity and coercivity, so they stay magnetised.
  39. 39. B — S = V × I (RMS) in VA or kVA. Generators and transformers are rated in kVA because their heating depends on current regardless of power factor.
  40. 40. A — V_out = V × R_bottom / (R_top + R_bottom) = 9 × 1/3 = 3 V.
  41. 41. C — With fewer electrons than protons the atom has a net positive charge and is called a positive ion (cation).
  42. 42. A — i = I_final(1 − e^(−t/τ)). At t = τ, 1 − e⁻¹ = 0.632.
  43. 43. B — Conductance G is the reciprocal of resistance: G = 1/R. Its unit is the siemens (S), formerly called the mho.
  44. 44. B — Tolerance bands: brown ±1 %, red ±2 %, gold ±5 %, silver ±10 %, no band ±20 %.
  45. 45. B — Pressure or strain on crystals such as quartz or barium titanate polarises them and a voltage appears across their faces. The effect is used in vibration pickups, microphones and pressure transducers.
  46. 46. A — Energy = P × t = 1 kW × 0.5 h = 0.5 kWh = 1.8 MJ.
  47. 47. B — Parallel capacitances add: C_T = 2 + 8 + 25 = 35 µF.
  48. 48. C — The stationary output winding needs no sliding contacts for the heavy load current and is easier to insulate. Only the low-power field current passes through slip rings (or none in a brushless design).
  49. 49. B — I_a = (V − E_b)/R_a = (24 − 22)/0.5 = 4 A.
  50. 50. B — Alternating current in the primary produces a changing flux in the core, which links the secondary and induces an EMF there.

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