22 Basic Electricity Practice Questions & Answers

1. 1. A 28-volt DC lamp is rated at 30 watts. Ignoring the change in filament resistance with temperature, what is the lamp's operating resistance?

   • A.About 840 ohms, since 28 volts multiplied by 30 watts is resistance
   • B.About 0.93 ohm, since 28 volts divided by 30 watts is resistance
   • C.About 1.07 ohms, since 30 watts divided by 28 volts is resistance
   • D.About 26 ohms, since resistance is voltage squared over power✓ Answer

   Power, voltage and resistance are linked by P = E squared divided by R, so R = E squared divided by P. Here 28 x 28 = 784, and 784 divided by 30 gives about 26 ohms. Dividing volts by watts (0.93) or watts by volts (1.07) produces current-based numbers, not resistance.

   Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, Fundamentals of Electricity and Electronics: Ohm's law and the power formulasReport a problem with this question

2. 2. A 40-volt source supplies a series circuit containing a 3-ohm, a 5-ohm, and a 12-ohm resistor. What is the voltage drop across the 12-ohm resistor?

   • A.13.3 volts, because 40 volts divides equally among the three resistors
   • B.40 volts, because every resistor in series sees the full source
   • C.24 volts, because 2 amperes flows through the 12-ohm resistor✓ Answer
   • D.20 volts, because the largest resistor in the string drops half the source

   In a series circuit the same current flows everywhere, and total resistance is the arithmetic sum: 3 + 5 + 12 = 20 ohms, so I = 40 / 20 = 2 amperes. The drop across any resistor is E = I x R, so 2 x 12 = 24 volts, and the three drops (6 + 10 + 24) add up to the 40-volt source.

   Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, Fundamentals of Electricity and Electronics: series DC circuits and voltage dropsReport a problem with this question

3. 3. Three lamps wired in series across a 24-volt bus have gone dark. With the bus powered, a voltmeter placed across the middle lamp reads 24 volts, and reads zero across each of the other two lamps. What does this indicate?

   • A.The middle lamp is open, so the full source voltage appears across the break✓ Answer
   • B.The middle lamp is shorted, so it alone drops the whole source voltage
   • C.The outer two lamps are open, which is why each of them reads zero
   • D.The voltmeter is on the wrong range and is reading the bus, not the lamp

   One open anywhere in a series circuit stops all current. With no current there is no I x R drop across the good lamps, so they read zero, while the entire source voltage appears across the break. A shorted lamp would read zero volts across itself and the other lamps would still light.

   Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, Fundamentals of Electricity and Electronics: troubleshooting opens in series circuitsReport a problem with this question

4. 4. Resistors of 4 ohms, 8 ohms, and 16 ohms are connected in parallel across a 24-volt source. What is the voltage across the 16-ohm resistor?

   • A.8 volts, because the 24 volts divides equally among the three branches
   • B.24 volts, because each branch is connected directly across the source✓ Answer
   • C.13.7 volts, because the largest resistor in a parallel group always drops the most
   • D.4.8 volts, because the voltage divides in proportion to each resistance

   Every branch of a parallel circuit is connected across the same two points, so each branch has the full source voltage regardless of its resistance. Only the branch currents differ: 6 amperes, 3 amperes and 1.5 amperes respectively. Voltage divides proportionally only in a series circuit.

   Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, Fundamentals of Electricity and Electronics: parallel DC circuitsReport a problem with this question

5. 5. A 28-volt bus supplies three parallel loads that draw 3 amperes, 5 amperes, and 1.5 amperes. What is the total current, and what is the total resistance of the combination?

   • A.3.2 amperes total, since the three branch currents are averaged
   • B.9.5 amperes total, with a total resistance of about 33.6 ohms
   • C.9.5 amperes total, with a total resistance of about 2.9 ohms✓ Answer
   • D.1.5 amperes total, since the smallest branch limits the whole bus

   Branch currents in a parallel circuit add: 3 + 5 + 1.5 = 9.5 amperes. Total resistance follows from Ohm's law, 28 / 9.5 = about 2.9 ohms, which is less than the smallest branch resistance (28 / 5 = 5.6 ohms). Adding branch resistances arithmetically, as in the 33.6-ohm answer, is the classic error.

   Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, Fundamentals of Electricity and Electronics: parallel DC circuits and total resistanceReport a problem with this question

6. 6. Three resistors of equal value are connected in parallel across a 48-volt source and together dissipate 192 watts. What is the resistance of each resistor?

   • A.108 ohms each, since the three branches must total 36 ohms
   • B.12 ohms each, since 48 volts divided by the 4 amperes gives 12 ohms
   • C.4 ohms each, since the source delivers a total of 4 amperes
   • D.36 ohms each, since each branch carries about 1.33 amperes✓ Answer

   Total current comes from P = I x E, so I = 192 / 48 = 4 amperes. Three equal branches split that evenly, 1.33 amperes each, and each branch has the full 48 volts across it, so R = 48 / 1.33 = 36 ohms. The 12-ohm figure is the total resistance of the combination, not the value of one resistor.

   Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, Fundamentals of Electricity and Electronics: power in parallel circuitsReport a problem with this question

7. 7. A 24-volt source feeds a 4-ohm resistor in series with a parallel pair made up of a 12-ohm and a 6-ohm resistor. What is the current through the 12-ohm resistor?

   • A.2 amperes, because the larger resistor takes the larger share of current
   • B.1 ampere, because the parallel pair drops 12 volts and that branch has 12 ohms✓ Answer
   • C.3 amperes, because the total circuit current flows in every branch alike
   • D.1.5 amperes, because the 3 amperes splits evenly between the two branches

   Reduce the parallel pair first: (12 x 6) / (12 + 6) = 4 ohms, so total resistance is 4 + 4 = 8 ohms and total current is 24 / 8 = 3 amperes. That current through the 4-ohm series resistor drops 12 volts, leaving 12 volts across the parallel pair, so the 12-ohm branch carries 12 / 12 = 1 ampere and the 6-ohm branch carries 2 amperes.

   Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, Fundamentals of Electricity and Electronics: series-parallel circuit analysisReport a problem with this question

8. 8. Four cabin reading lights are wired in parallel across a 28-volt bus. One of the lamps burns out and opens. What happens to the other three lamps and to the current drawn from the bus?

   • A.They burn brighter, because the remaining branches share more voltage
   • B.They all go out, because one open breaks the whole circuit path
   • C.They stay lit at 28 volts, and the total bus current decreases✓ Answer
   • D.They dim, because the lost branch raises the resistance of the others

   Each parallel branch has its own path to the source, so an open in one branch does not affect the others; they still see the full 28 volts and draw the same current as before. Removing a branch raises the total resistance of the combination, so the current drawn from the bus goes down by the amount the failed lamp was taking.

   Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, Fundamentals of Electricity and Electronics: parallel circuit behavior with an open branchReport a problem with this question

9. 9. The frequency applied to a coil of fixed inductance is doubled. What happens to the coil's inductive reactance?

   • A.It quadruples, because reactance varies with the square of frequency
   • B.It is halved, because reactance varies inversely with frequency
   • C.It is unchanged, because reactance is fixed by the inductance alone
   • D.It doubles, because reactance varies directly with frequency✓ Answer

   Inductive reactance is XL = 2 x pi x f x L, so it rises in direct proportion to both frequency and inductance. Doubling the frequency doubles XL. Capacitive reactance behaves the opposite way, falling as frequency rises, which is the source of the inverse-proportion distractor.

   Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, Fundamentals of Electricity and Electronics: inductance and inductive reactanceReport a problem with this question

10. 10. Two conductors are of the same material and at the same temperature. Which statement about the resistance of a conductor is correct?

    • A.Resistance rises with both the length and the cross-sectional area
    • B.Resistance rises with length and falls as cross-section grows✓ Answer
    • C.Resistance falls with length and rises as cross-section grows
    • D.Resistance depends only on the current carried, not on the wire size

    The resistance of a conductor is directly proportional to its length and inversely proportional to its cross-sectional area, and it also depends on the material and the temperature. That is why aircraft wire tables size conductors in circular mils and why a long run needs a larger wire to hold the voltage drop down.

    Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, Fundamentals of Electricity and Electronics: factors affecting the resistance of a conductorReport a problem with this question

11. 11. The current-carrying capacity listed for a single wire in free air is reduced when that same wire is run inside a bundle or a conduit. What is the reason for this derating?

    • A.Heat escapes less readily from a wire inside a bundle, so a given current makes it run hotter✓ Answer
    • B.The magnetic fields of adjacent wires oppose one another and cut the usable current
    • C.Bundling raises the resistance of each conductor, so less current may be carried
    • D.The insulation is thinner on bundled wire, so a smaller rating has to be used

    A conductor's rating is set by the temperature its insulation can stand. Current produces I squared R heating, and a wire buried in a bundle or shut inside conduit cannot radiate or convect that heat away as a single wire in open air can, so the same current drives the conductor to a higher temperature and the rating must be reduced.

    Source: AC 43.13-1B, Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair, wire current-carrying capacity and bundle deratingReport a problem with this question

12. 12. When a fuse or circuit breaker rating is selected for an aircraft circuit, what is the protective device chosen primarily to protect?

    • A.The wire, which must open the circuit before the conductor overheats✓ Answer
    • B.The connected equipment, which must be shut off before it is damaged
    • C.The generator, which must not be loaded beyond its rated output
    • D.The control switch, which must not carry more than its own rating

    Circuit protection is sized to the conductor: the fuse or breaker must open on a fault before the wire's insulation is damaged by heat, because a burning wire inside a bundle is far more dangerous than a failed component. Equipment protection, when needed, is a separate function built into the equipment itself.

    Source: AC 43.13-1B, Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair, circuit protection devicesReport a problem with this question

13. 13. Which statement about resettable circuit breakers installed in aircraft is correct?

    • A.A tripped breaker should be reset again and again until the circuit stays on
    • B.Automatic-reset types are preferred in aircraft because they restore a circuit fast
    • C.Automatic-reset types are not used in aircraft; a tripped breaker is reset by hand✓ Answer
    • D.A tripped breaker has to be replaced, because a breaker cannot be reset at all

    A circuit breaker opens at a predetermined current and can be reset, unlike a fuse or current limiter, which must be replaced. Automatic-reset breakers are not acceptable for aircraft because they would repeatedly re-energize a faulted circuit; resetting is done manually and only once, since repeated resetting risks circuit damage, fire or explosion.

    Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, Fundamentals of Electricity and Electronics: circuit protection devices, circuit breakersReport a problem with this question

14. 14. Why must an ammeter never be connected directly across a battery or other voltage source?

    • A.Its internal resistance is very high, so it would read far below the true value
    • B.Its internal resistance is very low, so it would pass a damaging current✓ Answer
    • C.It would indicate the source voltage in place of the circuit current
    • D.It would slowly discharge the battery and then give a low reading

    An ammeter is built with very low internal resistance so that inserting it in series does not change the circuit it is measuring. Placed straight across a source, that low resistance is effectively a short circuit, and the resulting current will burn out the movement or its shunt.

    Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, Fundamentals of Electricity and Electronics: ammeter use and precautionsReport a problem with this question

15. 15. How are the ranges of a moving-coil ammeter and a moving-coil voltmeter extended?

    • A.A multiplier in series for the ammeter, a shunt in parallel for the voltmeter
    • B.A shunt in parallel for the ammeter, a multiplier in series for the voltmeter✓ Answer
    • C.A shunt in series for the ammeter, a multiplier in parallel for the voltmeter
    • D.A larger coil for both meters, because resistors cannot change a meter range

    An ammeter is connected in series with the load, and its range is raised by a shunt, a low-value resistor in parallel with the movement that carries most of the current. A voltmeter is connected in parallel with the component being measured, and its range is raised by a multiplier, a high-value resistor in series with the movement.

    Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, Fundamentals of Electricity and Electronics: electrical measuring instruments, shunts and multipliersReport a problem with this question

16. 16. Why must a circuit be de-energized before an ohmmeter is connected to it?

    • A.The meter supplies its own test voltage, so outside voltage falsifies readings and can ruin it✓ Answer
    • B.The meter has to be zeroed with the leads shorted, which cannot be done on a live circuit
    • C.The circuit voltage would add itself to the resistance shown on the nonlinear scale
    • D.The ohms scale reads from right to left and its zero end reverses under load voltage

    An ohmmeter measures by sending a known current from its own internal battery through the unknown resistance and reading the deflection. Any voltage already present in the circuit adds to or opposes that internal source, so the indication is meaningless, and enough external voltage will destroy the movement. The component should also be isolated, because parallel paths read low.

    Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, Fundamentals of Electricity and Electronics: ohmmeter use, zeroing and precautionsReport a problem with this question

17. 17. A lead-acid aircraft battery is being checked with a hydrometer. Which statement about the procedure and the readings is correct?

    • A.Specific gravity is read right after topping up so the added water mixes in well
    • B.Specific gravity rises as the battery discharges, and it is read after water is added
    • C.Specific gravity stays constant while charge is drawn, so any reading is valid
    • D.Specific gravity falls as the battery discharges, and is read before water is added✓ Answer

    In a lead-acid cell the sulfuric acid is consumed as the battery discharges and water is formed, so the specific gravity of the electrolyte drops in step with the state of charge. Adding distilled water first dilutes the electrolyte and the sample no longer represents the charge, which is why the hydrometer reading is always taken before water is added.

    Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, aircraft batteries: lead-acid cell chemistry and hydrometer testingReport a problem with this question

18. 18. How does the electrolyte of a nickel-cadmium battery behave compared with that of a lead-acid battery, and when should distilled water be added to the nickel-cadmium battery?

    • A.Its specific gravity stays nearly constant, and water is added when fully charged✓ Answer
    • B.Its specific gravity falls as it discharges, and water is added when it reads low
    • C.Its specific gravity stays nearly constant, and water is added when fully discharged
    • D.Its specific gravity rises as it discharges, and water is added before every charge

    The potassium hydroxide electrolyte of a nickel-cadmium cell takes no lasting part in the chemical change, so its specific gravity does not track the state of charge the way sulfuric acid does. The electrolyte level, however, falls during discharge and is highest at the end of a charge, so water is added only with the battery fully charged or the cell will overflow later.

    Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, aircraft batteries: nickel-cadmium cell electrolyte and servicingReport a problem with this question

19. 19. Which type of DC motor develops the greatest starting torque, and why does that make it suitable for an engine starter or a landing gear actuator?

    • A.The series-wound motor, because field and armature carry the same heavy current at zero speed✓ Answer
    • B.The shunt-wound motor, because its field is across the line and holds full strength
    • C.The compound motor, because its two fields oppose and limit the starting current
    • D.The induction motor, because its rotor slips freely until the load starts moving

    In a series motor the field winding is in series with the armature, so the same current flows in both. At the instant of starting the armature is not turning and produces no counter EMF, so the current is at its maximum and both field strength and armature current are at their highest, which is exactly the condition for maximum torque.

    Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, Fundamentals of Electricity and Electronics: DC motors, series, shunt and compound typesReport a problem with this question

20. 20. A meter reading effective (rms) values shows 115 volts in an alternating-current circuit. What is the peak value of that voltage?

    • A.About 81 volts, since peak equals the effective value times 0.707
    • B.About 163 volts, since peak equals the effective value times 1.414✓ Answer
    • C.About 115 volts, since effective and peak are the same in a sine wave
    • D.About 230 volts, since the peak is always twice the effective value

    For a sine wave the effective value is 0.707 times the peak, so the peak is 1.414 times the effective value: 115 x 1.414 = about 163 volts. The effective value is the one that does the same heating work as an equal direct current, and it is what AC meters and system ratings normally show.

    Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, Fundamentals of Electricity and Electronics: alternating current, peak and effective valuesReport a problem with this question

21. 21. A transformer has 200 turns on the primary and 800 turns on the secondary, and 24 volts AC is applied to the primary. What is the secondary voltage, and what happens to the available current?

    • A.24 volts, because a transformer changes current but never changes voltage
    • B.96 volts, with the available secondary current raised in the same proportion
    • C.6 volts, with the available secondary current raised in the same proportion
    • D.96 volts, with the available secondary current cut in the same proportion✓ Answer

    In an ideal transformer the voltage ratio equals the turns ratio, so 800 / 200 = 4 and the secondary delivers 4 x 24 = 96 volts. Power out cannot exceed power in, so a step-up in voltage is matched by a step-down in available current, and the device works only on alternating current because it depends on mutual induction.

    Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, Fundamentals of Electricity and Electronics: transformers and turns ratioReport a problem with this question

22. 22. What property of a semiconductor diode makes it useful as a rectifier?

    • A.It stores charge on one half cycle and then gives it back on the next half cycle
    • B.It keeps the same voltage drop across itself no matter which way it happens to be biased
    • C.It conducts when forward biased and blocks when reverse biased, making AC into pulsating DC✓ Answer
    • D.It raises the frequency of the applied alternating current up to a usable value

    A diode is a one-way device: with the anode positive with respect to the cathode it conducts, and with the polarity reversed it blocks. Feeding alternating current through it therefore removes one half of each cycle, leaving pulsating direct current, which is what rectification means. Storing and returning charge describes a capacitor, not a diode.

    Source: FAA-H-8083-30, Aviation Maintenance Technician Handbook-General, Fundamentals of Electricity and Electronics: semiconductors, diodes and rectifiersReport a problem with this question

Practice questions based on 14 CFR Parts 43 and 65 and the FAA Aviation Maintenance Technician Handbook—General (FAA-H-8083-30). This site is not affiliated with or endorsed by the Federal Aviation Administration. This bank covers the GENERAL written test only; the Airframe and Powerplant written tests and the oral and practical exams are separate. Torque values, servicing quantities, corrosion rework limits, and inspection criteria always come from the manufacturer's current maintenance data and the applicable airworthiness directives — never from a practice test. Confirm current eligibility and testing requirements with the FAA before you test. About the A&P mechanic certificate →