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Module 4 Electronic fundamentals: 50 practice questions

Real EASA paper: B1.1 20 Q / 25 min · B1.2 20 Q / 25 min · B1.3 20 Q / 25 min · B2 40 Q / 50 min · B2L 40 Q / 50 min · B3 20 Q / 25 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. In a bridge rectifier, the peak inverse voltage across each non-conducting diode is approximately

    1. A. the RMS value of the secondary voltage
    2. B. twice the peak secondary voltage
    3. C. the peak value of the secondary voltage

  2. 2. Ground planes on a PCB help to:

    1. A. reduce noise and give a low-impedance return path
    2. B. increase the impedance of signal tracks
    3. C. carry the main power supply current

  3. 3. The 'dead band' of a servo is:

    1. A. the maximum speed that the output can reach
    2. B. the input range over which the output does not respond
    3. C. the time the output takes to reach full travel

  4. 4. Which description best fits an integrated circuit (IC)?

    1. A. a single transistor in a plastic case
    2. B. a printed board carrying discrete parts
    3. C. a complete circuit of many components formed on one chip

  5. 5. The green (or other coloured) coating over most of a PCB is the

    1. A. solder mask
    2. B. silk-screen legend
    3. C. conformal coating

  6. 6. A 'follow-up' in an autopilot servo provides:

    1. A. the authority limit that restricts servo travel
    2. B. feedback of surface or servo position to cancel the command
    3. C. the trim command sent to the elevator tab

  7. 7. Approximately what base-emitter voltage is needed to turn on a silicon transistor?

    1. A. 0.6 to 0.7 V
    2. B. 0.2 to 0.3 V
    3. C. 5 to 6 V

  8. 8. Excessive heat applied while desoldering a component from a PCB can cause

    1. A. increased track conductivity
    2. B. lifted pads and delamination
    3. C. the laminate to become conductive

  9. 9. In a servo system, the error signal is

    1. A. the difference between demanded and actual position
    2. B. the supply voltage to the motor
    3. C. the sum of demanded and actual position

  10. 10. An op amp used as a comparator

    1. A. switches its output according to which input is larger
    2. B. requires a capacitor in the feedback loop
    3. C. gives an output equal to the input difference

  11. 11. Crosstalk between PCB tracks is caused by

    1. A. coupling between adjacent tracks
    2. B. the resistance of each track alone
    3. C. the colour of the solder mask

  12. 12. A closed-loop servomechanism differs from an open-loop system because it:

    1. A. uses a more powerful motor than the open-loop type
    2. B. responds only to step inputs, not to ramps
    3. C. compares output with input using feedback and corrects the error

  13. 13. The barrier potential across an unbiased silicon P-N junction is approximately

    1. A. 1.5 V
    2. B. 0.7 V
    3. C. 0.3 V

  14. 14. Why are multilayer PCBs difficult to repair?

    1. A. They contain no copper at all
    2. B. Inner tracks cannot be reached
    3. C. They can only be fitted once

  15. 15. Overshoot in a servo system is when

    1. A. the output moves past the demanded position
    2. B. the output never moves
    3. C. the output stops short with a constant error

  16. 16. A Zener diode is designed to operate

    1. A. in the reverse breakdown region
    2. B. only below its knee voltage
    3. C. only in the forward direction

  17. 17. A 'cold' solder joint on a PCB appears

    1. A. bright and smoothly concave
    2. B. completely covered by solder mask
    3. C. dull and grainy with poor wetting

  18. 18. An E and I transformer (E-core pickoff) is used to

    1. A. step up the aircraft AC voltage
    2. B. rectify AC for the servo motors
    3. C. detect small armature movements

  19. 19. A silicon rectifier diode has a forward voltage drop of 0.8 V when carrying 20 A. How much power does it dissipate?

    1. A. 25 W
    2. B. 320 W
    3. C. 16 W

  20. 20. Before handling a PCB containing static-sensitive devices, the technician should

    1. A. remove it from its shielded bag and check it
    2. B. wear an earthed wrist strap
    3. C. clean the board with a dry cloth

  21. 21. A series diode clipper removes

    1. A. the half of the waveform that reverse-biases the diode
    2. B. the high-frequency components of the signal
    3. C. the average DC level of the waveform

  22. 22. Surface-mount devices (SMDs) differ from through-hole components in that they:

    1. A. always need a plated-through hole beneath each pad
    2. B. can only be fitted on the top side of the board
    3. C. are soldered to pads on the board surface without leads through holes

  23. 23. In the schematic symbol of a diode, the arrow (triangle) points toward

    1. A. the cathode, in the direction of electron flow
    2. B. the cathode, in the direction of conventional current
    3. C. the anode, in the direction of conventional current

  24. 24. Track width on a PCB is chosen mainly according to

    1. A. the colour of the solder mask
    2. B. the number of components on the board
    3. C. the current the track must carry

  25. 25. RC (capacitive) coupling between amplifier stages

    1. A. passes AC signals but blocks DC bias levels
    2. B. provides impedance matching like a transformer
    3. C. passes DC and AC equally

  26. 26. The main advantage of PCBs over point-to-point wiring is

    1. A. easy on-aircraft repair of tracks
    2. B. higher voltage capability in all cases
    3. C. consistent, compact and repeatable construction

  27. 27. An emitter resistor in a common-emitter stage improves bias stability because it

    1. A. provides positive feedback to the base
    2. B. gives negative feedback against I_C changes
    3. C. increases the AC voltage gain

  28. 28. A linear integrated circuit differs from a digital IC in that it

    1. A. handles only two voltage levels
    2. B. cannot contain transistors
    3. C. processes continuously varying signals

  29. 29. The arrow on a transistor symbol shows the direction of

    1. A. conventional current in the emitter
    2. B. electron flow in the collector
    3. C. the signal from input to output

  30. 30. The maximum forward current rating of a diode is limited mainly by

    1. A. the heat generated at the junction
    2. B. the reverse leakage current
    3. C. the barrier potential

  31. 31. A silicon diode fails open-circuit. On an analogue ohmmeter it will read

    1. A. low resistance in both directions
    2. B. high resistance in both directions
    3. C. low one way and high the other

  32. 32. In a non-inverting op-amp amplifier the input impedance is

    1. A. very high
    2. B. almost zero
    3. C. equal to R_in

  33. 33. An LED emitting infrared light is typically used in

    1. A. general cabin lighting
    2. B. optocouplers and remote sensing
    3. C. voltage reference circuits

  34. 34. Thermal stabilisation of a transistor amplifier can be improved by

    1. A. removing all resistors from the base circuit
    2. B. using an emitter resistor and a stable divider bias
    3. C. increasing the supply voltage

  35. 35. Light is produced by an LED when the device is

    1. A. reverse biased beyond breakdown
    2. B. forward biased, as carriers recombine
    3. C. left unbiased in darkness

  36. 36. A push-pull amplifier using two class B transistors has an advantage over a single class A transistor because

    1. A. it produces no distortion at all
    2. B. it needs no DC supply
    3. C. it is much more efficient

  37. 37. Trivalent atoms added to silicon are called acceptors because they

    1. A. accept electrons, creating holes
    2. B. accept protons from neighbouring atoms
    3. C. donate free electrons to the crystal

  38. 38. Which material is NOT used as a semiconductor for diodes?

    1. A. Silicon
    2. B. Copper
    3. C. Germanium

  39. 39. An op-amp differentiator has a triangular wave applied. The output is

    1. A. a square wave
    2. B. a sine wave
    3. C. a triangular wave of higher amplitude

  40. 40. A digital multimeter on the diode-test range reads about 0.6 V one way and OL the other across a diode. The diode is

    1. A. open-circuited
    2. B. short-circuited
    3. C. serviceable

  41. 41. On a diode forward characteristic, current remains very small until the

    1. A. leakage current has stopped
    2. B. peak inverse voltage is reached
    3. C. knee (threshold) voltage is reached

  42. 42. Power transistors are often mounted on heat sinks with an insulating washer because

    1. A. the case is always connected to the base
    2. B. the washer increases current gain
    3. C. the case is often connected to the collector

  43. 43. When a P-N junction is formed, a depletion region develops because

    1. A. an external voltage is always applied to it
    2. B. the junction region becomes heavily doped
    3. C. carriers diffuse across the junction and recombine

  44. 44. Power dissipated in a diode is calculated as

    1. A. forward voltage drop × forward current
    2. B. forward current ÷ forward voltage drop
    3. C. peak inverse voltage × forward current

  45. 45. Two amplifier stages with voltage gains of 20 and 40 are connected in cascade. What is the overall voltage gain?

    1. A. 800
    2. B. 60
    3. C. 400

  46. 46. A common-emitter stage has a collector resistor of 5.5 kΩ and an unbypassed emitter resistor of 0.47 kΩ. What is the approximate magnitude of its voltage gain?

    1. A. 11.7
    2. B. 0.09
    3. C. 2.58

  47. 47. What ripple frequency appears at the output of a half-wave rectifier running from a 50 Hz supply?

    1. A. 100 Hz
    2. B. 25 Hz
    3. C. 50 Hz

  48. 48. Why is a resistor often placed in parallel with the capacitor of a practical integrator?

    1. A. To raise the integration rate
    2. B. To limit DC gain so offset cannot saturate it
    3. C. To make it act as a differentiator

  49. 49. A diode used with an AC supply at 400 Hz must have a suitable

    1. A. colour code
    2. B. frequency (recovery) rating
    3. C. barrier potential of 1.5 V

  50. 50. A phototransistor differs from an ordinary transistor because its

    1. A. collector current cannot exceed base current
    2. B. base current is produced by light
    3. C. emitter is made of transparent glass

Answer key

  1. 1. C — Each reverse-biased pair shares the secondary voltage, so each diode sees about V_pk, allowing lower-rated diodes than a centre-tap circuit.
  2. 2. A — A continuous copper ground plane minimises loop area and interference and helps spread heat.
  3. 3. B — A small dead band prevents hunting due to noise, but too large a dead band reduces accuracy.
  4. 4. C — Transistors, diodes, resistors and small capacitors are fabricated together on a silicon chip, giving small size, low power and high reliability.
  5. 5. A — Solder mask covers the copper except at pads, preventing solder bridges and protecting tracks.
  6. 6. B — The follow-up signal opposes the command so the servo stops when the surface has moved by the commanded amount.
  7. 7. A — The base-emitter junction behaves like a silicon diode, conducting at about 0.6-0.7 V.
  8. 8. B — Adhesive holding copper to the laminate weakens with heat, so pads and tracks lift; prolonged heat can separate layers.
  9. 9. A — Error = demand − feedback. It is amplified to drive the motor toward zero error.
  10. 10. A — With no negative feedback, the output swings to the positive or negative saturation level. Uses include level detection and go/no-go circuits.
  11. 11. A — Long parallel tracks couple signals; spacing, ground planes and routing reduce crosstalk.
  12. 12. C — Closed loop: command → error detector → amplifier → motor → output, with feedback of the output to the error detector.
  13. 13. B — The ions in the depletion region set up a potential barrier: about 0.6-0.7 V for silicon and 0.2-0.3 V for germanium.
  14. 14. B — Damage to inner tracks or plated vias usually means board replacement.
  15. 15. A — Inertia carries the load past the null. Damping reduces overshoot.
  16. 16. A — Zener diodes are heavily doped to give a sharp, stable breakdown voltage. In breakdown the voltage stays nearly constant over a wide current range.
  17. 17. C — Insufficient heat gives a poorly wetted joint that may crack and cause intermittent faults.
  18. 18. C — The primary on the centre leg induces equal, opposing voltages in outer coils at null; moving the I-bar unbalances them.
  19. 19. C — P = V_F × I_F = 0.8 × 20 = 16 W.
  20. 20. B — An earthed wrist strap at an ESD-protected workstation keeps the technician at the same potential as the board.
  21. 21. A — A series diode passes one polarity and blocks the other, so the output is clipped at about zero (plus the diode drop).
  22. 22. C — SMDs sit on pads and are reflow-soldered; they allow both sides to be populated and smaller assemblies.
  23. 23. B — The triangle is the anode side and the bar is the cathode. Conventional current flows in the direction of the arrow when the diode is forward biased.
  24. 24. C — Wider or thicker copper has lower resistance and heating; spacing between tracks is set by the voltage difference.
  25. 25. A — The coupling capacitor lets each stage be biased independently but limits low-frequency response.
  26. 26. C — Tracks are produced photographically, so every board is identical, wiring errors are avoided and assemblies are compact and light.
  27. 27. B — If I_C rises, the voltage across R_E rises, reducing V_BE and pulling I_C back down (DC negative feedback).
  28. 28. C — Linear (analogue) ICs, such as op amps and voltage regulators, operate over a continuous range; digital ICs switch between defined logic levels.
  29. 29. A — Like a diode symbol, the arrow shows conventional current across the forward-biased base-emitter junction.
  30. 30. A — Forward current produces P = V_F × I_F in the junction. Exceeding the rating overheats and destroys the junction; large rectifiers use metal cases and heat sinks.
  31. 31. B — An open junction blocks current in both directions.
  32. 32. A — The signal drives the + input directly, which draws almost no current; in the inverting amplifier, R_in sets the input impedance.
  33. 33. B — IR LEDs are paired with photodiodes or phototransistors in optocouplers, position sensors and encoders.
  34. 34. B — Negative DC feedback via R_E and a stiff divider limit collector current rise with temperature; diodes or thermistors can also compensate.
  35. 35. B — When electrons cross the junction and fall into holes they release energy; in LED materials such as gallium arsenide phosphide this is released as light.
  36. 36. C — Each transistor draws current only when amplifying its half-cycle, so standby dissipation is very low.
  37. 37. A — Each acceptor atom takes an electron from a neighbouring bond, leaving a mobile hole.
  38. 38. B — Silicon, germanium and compounds such as gallium arsenide are semiconductors. Copper is a metallic conductor.
  39. 39. A — A triangle has constant positive and negative slopes; their derivatives are constant levels, forming a square wave.
  40. 40. C — The diode-test range passes a small current and displays the forward drop (about 0.5-0.7 V for silicon); reverse shows over-range.
  41. 41. C — Below about 0.6-0.7 V (silicon) the barrier prevents significant conduction; above the knee the current rises steeply for small increases in voltage.
  42. 42. C — The metal tab or case normally connects to the collector; an insulating washer (with thermal compound) isolates it electrically while conducting heat.
  43. 43. C — Diffusion and recombination leave fixed positive donor ions on the N side and negative acceptor ions on the P side. This region is depleted of free carriers.
  44. 44. A — P = V_F × I_F. For a silicon rectifier carrying 10 A with 0.8 V drop, 8 W must be removed as heat.
  45. 45. A — Cascaded gains multiply: 20 × 40 = 800.
  46. 46. A — With an unbypassed emitter resistor, |A_v| ≈ R_C/R_E = 5.5/0.47 = 11.7 (the output is inverted).
  47. 47. C — A half-wave rectifier gives one pulse per input cycle, so f_ripple = f = 50 Hz.
  48. 48. B — Without it, small input offsets are integrated indefinitely until the output saturates; the resistor sets a finite DC gain.
  49. 49. B — At higher frequencies a slow diode cannot switch off quickly enough, causing losses. Diodes are rated for maximum frequency or reverse recovery time.
  50. 50. B — Light creates carriers in the base-collector region, acting like base current that is then amplified.

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