Fundamentals of Electricity and Electronics is the ACS subject area where candidates lose points for arithmetic reasons rather than knowledge reasons. You are asked to apply Ohm's law, combine resistors in series and parallel, predict what a meter reads when it is wired into a circuit, and say what capacitors, fuses and circuit breakers do in an aircraft electrical system. The math is simple; the setup is where people go wrong. This page lays out what the area covers, the three misreadings that cost the most marks, and free practice questions drawn from the same General bank.
Written by the AMTprep editorial team · Published · Last reviewed
Written against the FAA primary sources cited at the foot of this page.
This is the electrical theory half of the General written, and the bank tracks FAA-H-8083-30 closely. Expect three kinds of item. First, direct calculation: the current in a circuit with a 12-volt source across a 6-ohm resistance, the total resistance of two 10-ohm resistors in parallel, the total voltage of three 1.5-volt cells wired in series. The numbers are chosen to come out clean, so a messy answer usually means you inverted the formula. Second, circuit behavior with no numbers at all: how current compares at different points in a series circuit, how voltage divides across unequal resistances, which quantity stays constant in a series string and which stays constant across a parallel one. Third, hardware and instrumentation: how a voltmeter is connected to read the drop across a resistor, which property of a conductor raises its resistance, what a capacitor does, and why a fuse or circuit breaker is in the circuit at all. These are written as recall or single-step application items, not multi-stage design problems, so the whole area rewards knowing E = I x R cold and knowing what stays constant where. FAA-H-8083-30 covers the same ground in its electricity chapters, including the four factors that set conductor resistance, meter connection, capacitance and circuit protection. Aircraft context such as bus systems, bonding and protection sizing sits on top of that foundation and shows up in the applied questions.
ACS AM.I.A is tested on the FAA General written test, one of 1,558 ACS-tagged questions in the General bank. Every question tagged to this area carries a worked rationale and its FAA handbook reference, so you can drill the code itself rather than the whole test.
According to Ohm's law, what current flows in a circuit having a 12-volt source connected across a 6-ohm resistance?
In a series circuit containing three resistors, how does the current compare at different points in the circuit?
What is the total resistance of two 10-ohm resistors connected in parallel?
How should a voltmeter be connected to measure the voltage drop across a resistor?
Which property of a conductor increases its electrical resistance?
What is the function of a capacitor in an electrical circuit?
In aircraft electrical systems, what is the primary purpose of a fuse or circuit breaker?
What is the total voltage of three 1.5-volt cells connected in series?
What is the power dissipated by a load drawing 3 amperes at 24 volts?
What happens to total resistance in a circuit as more resistors are added in parallel?
The particle in the nucleus of an atom that carries a positive charge is the
The nucleus of an atom carries what overall electrical charge?
Most of an atom's mass is contained in the
In an electrical insulator, the electrons are
Which temperature-sensing component changes its electrical resistance with temperature and can be used where the source is too cool to drive a thermocouple?
0.000006 volts can be written as
0.004 amperes can be written as
When clamping a wire bundle that contains coaxial cable, why must the coaxial cable not be crushed or distorted?
On a printed circuit board (PCB), the copper conductor tracks are etched
When soldering a wire to an electrical terminal, the technician should tin
When the handle of a megohmmeter (megger) is cranked with the test leads held apart, the pointer will
To perform an insulation-resistance test on wiring rated for a 115-volt circuit, the technician would normally use a megohmmeter (megger) rated at
A 250-volt megohmmeter (megger) should NOT be used to test
One megohm is equal to
The leads supplied with a bonding/continuity tester used to measure very low resistances
The test instrument normally used to perform a continuity check on an electrical cable is
A circuit reads 400 volts and 20 amperes, while a power meter shows a true power of 4 kW. The power factor is
To measure the current flowing in a circuit, an ammeter is connected
A 3 1/2-digit digital multimeter will display a maximum reading of
When checking a wire with an ohmmeter, an open circuit is indicated by a reading of
Which function of a multimeter requires an internal battery as a power source?
On a multimeter, which color test lead is normally connected to the COMMON (negative) socket?
To measure the voltage drop across a component, the voltmeter is connected in
A basic moving-coil multimeter can measure alternating current because it includes a
A crimped electrical connection is suspected of being high-resistance. How can this be verified without disconnecting the circuit?
Which instrument best locates a discontinuity or short along a long coaxial cable?
A live AC circuit is to be checked for an open circuit using a
A multiplier resistance is used to extend the working range of a
A typical AC voltmeter that uses a rectifier and a moving-coil movement responds to the
A hydrometer is used to
A pyrometer is best described as a
A hygrometer is an instrument used to
To measure alternating current with a moving-coil (d'Arsonval) meter movement, the current
To extend the range of a milliammeter so it can read a larger current at full-scale deflection, you would
The internal resistance of a voltmeter should be
The internal resistance of an ammeter should be
On an analog ohmmeter, the scale is
To perform a continuity test on a conductor, you would use
In a moving-coil (permanent-magnet moving-coil) meter, the deflecting force on the pointer is produced by
In a moving-coil (D'Arsonval) meter movement, the force that returns the pointer to zero when no current flows is called the
ACS code: AM.I.A
Correct answer: 2 amperes.
Rationale: Ohm's law states I = E/R. Dividing the 12-volt source by the 6-ohm resistance gives 12 / 6 = 2 amperes. The 18-ampere choice incorrectly adds voltage and resistance, and 72 amperes incorrectly multiplies them.
ACS code: AM.I.A
Correct answer: It is the same through every resistor.
Rationale: A series circuit provides only one path for current flow, so the same current passes through every component. Voltage divides across the resistors in proportion to their values, but the current is identical at all points, as described for series circuits in the handbook.
ACS code: AM.I.A
Correct answer: 5 ohms.
Rationale: For two equal resistors in parallel, total resistance equals the value of one resistor divided by the number of resistors: 10 / 2 = 5 ohms. Parallel resistance is always less than the smallest individual resistor, so 10 ohms or 20 ohms cannot be correct.
ACS code: AM.I.A
Correct answer: In parallel with the resistor.
Rationale: A voltmeter has very high internal resistance and is connected in parallel (across) the component being measured so it reads the potential difference without disturbing circuit current. An ammeter, by contrast, is connected in series. Connecting a voltmeter in series would not read the drop correctly.
ACS code: AM.I.A
Correct answer: Increasing its length.
Rationale: Resistance of a conductor is directly proportional to its length, so a longer wire has more resistance. Increasing cross-sectional area (diameter) lowers resistance, and for most conductors resistance decreases as temperature decreases, so those choices reduce rather than increase resistance.
ACS code: AM.I.A
Correct answer: To store an electrical charge.
Rationale: A capacitor consists of two plates separated by a dielectric and stores an electrical charge as an electrostatic field between the plates. Rectifiers convert AC to DC, and transformers change voltage levels, so those functions belong to other components.
ACS code: AM.I.A
Correct answer: To protect the circuit from excessive current.
Rationale: A fuse or circuit breaker opens the circuit when current exceeds a safe value, protecting wiring and components from overheating damage. It does not raise voltage or store energy; those are functions of transformers and capacitors respectively.
ACS code: AM.I.A
Correct answer: 4.5 volts.
Rationale: Cells connected in series add their individual voltages, so three 1.5-volt cells produce 1.5 + 1.5 + 1.5 = 4.5 volts. Cells in parallel keep the same voltage (1.5 volts) but add capacity, so the other choices do not apply to a series connection.
ACS code: AM.I.A
Correct answer: 72 watts.
Rationale: Electrical power equals voltage times current, P = E × I, so 24 volts × 3 amperes = 72 watts. The 8-watt answer incorrectly divides voltage by current, and 27 watts incorrectly adds them.
ACS code: AM.I.A
Correct answer: It decreases.
Rationale: Each additional parallel branch provides another path for current, so total circuit resistance decreases and the total current the source must supply increases. This is the opposite of a series circuit, where adding resistors raises total resistance.
ACS code: AM.I.A
Correct answer: proton.
Rationale: Protons are the positively charged particles located in the nucleus of an atom. Electrons carry an equal and opposite negative charge orbiting the nucleus, while neutrons carry no charge, so a balanced atom is electrically neutral overall.
ACS code: AM.I.A
Correct answer: Positive.
Rationale: The nucleus contains positively charged protons together with neutral neutrons, so the nucleus as a whole carries a positive charge. The negatively charged electrons are not in the nucleus but orbit around it.
ACS code: AM.I.A
Correct answer: nucleus.
Rationale: Nearly all of an atom's mass is concentrated in the small central nucleus, which contains the protons and neutrons. The orbiting electrons have negligible mass, so the nucleus accounts for essentially all of the atom's mass.
ACS code: AM.I.A
Correct answer: tightly bound to their atoms.
Rationale: In an insulator the outer (valence) electrons are tightly bound to their atoms and are not free to move, so the material resists current flow. Conductors have loosely bound or free electrons that allow charge to move easily.
ACS code: AM.I.A
Correct answer: Thermistor.
Rationale: A thermistor changes its electrical resistance with temperature and is self-contained, so it works where a source is too cool to generate a usable thermocouple voltage. A thermostat is a switching device and a voltmeter measures potential difference, so neither senses low-level temperature in this way.
ACS code: AM.I.A
Correct answer: 6 microvolts.
Rationale: The prefix micro means 10^-6, so 6 microvolts = 6 x 10^-6 = 0.000006 volts. Milli is 10^-3 (0.006 V) and nano is 10^-9, so only microvolts fits the magnitude. See FAA-H-8083-30, Fundamentals of Electricity and Electronics.
ACS code: AM.I.A
Correct answer: 4 mA.
Rationale: The prefix milli means one-thousandth, so 1 mA = 0.001 A. Dividing 0.004 A by 0.001 gives 4, so 0.004 amperes equals 4 mA. The kilo answer is wrong because kilo means a thousand times larger, not smaller. See FAA-H-8083-30, Fundamentals of Electricity and Electronics.
ACS code: AM.I.A
Correct answer: Distortion changes the dielectric spacing and alters the cable's characteristic impedance.
Rationale: A coaxial cable relies on a precise, uniform spacing between the inner conductor and outer shield, set by the dielectric. Crushing or distorting the cable changes that spacing and the dielectric, altering the cable's characteristic impedance and degrading the signal. Clamps are tightened only enough to support the bundle without deforming the cable.
ACS code: AM.I.A
Correct answer: before any components are installed.
Rationale: On a printed circuit board the copper tracks are chemically etched onto the laminate during board manufacture, before any components are installed. Components are inserted and soldered to the already-etched tracks afterward, so etching cannot take place after installation or after soldering.
ACS code: AM.I.A
Correct answer: both the end of the wire and the terminal.
Rationale: Good soldering practice is to pre-tin both the wire end and the terminal before joining them. Tinning coats each part with a thin layer of solder, wetting the surfaces so that a sound, low-resistance joint forms when they are brought together and heated. Tinning only one part risks a cold or high-resistance joint.
ACS code: AM.I.A
Correct answer: remain at the infinity end of the scale.
Rationale: With the megger leads held apart the circuit is open, presenting effectively infinite resistance. As the handle is cranked and voltage is generated, no current can flow across the open gap, so the pointer remains at the infinity end of the ohms scale rather than deflecting toward zero.
ACS code: AM.I.A
Correct answer: 250 volts.
Rationale: Insulation resistance is tested at a voltage related to the circuit's working voltage, commonly about twice it, so 115-volt wiring is checked with a 250-volt megger. A 115-volt tester would not adequately stress the insulation, while a 500-volt unit could over-stress insulation rated only for low-voltage service (FAA-H-8083-30, Fundamentals of Electricity and Electronics).
ACS code: AM.I.A
Correct answer: electronic equipment.
Rationale: A 250-volt megger applies a high test voltage to measure insulation resistance, which can break down semiconductors and other delicate components. For that reason it is restricted to robust wiring and machines, while sensitive electronic/avionics equipment must be checked only with low-voltage instruments (FAA-H-8083-30, Fundamentals of Electricity and Electronics).
ACS code: AM.I.A
Correct answer: 1,000,000 ohms.
Rationale: The prefix mega- means one million, so one megohm equals 1,000,000 ohms. One thousand ohms is one kilohm, and 100,000 ohms is only one-tenth of a megohm (FAA-H-8083-30, Fundamentals of Electricity and Electronics).
ACS code: AM.I.A
Correct answer: have critical fixed lengths, and their resistance is accounted for in calibration.
Rationale: A bonding tester measures very low resistances, so the resistance of its own leads is significant. The leads are of fixed, critical length and the instrument is calibrated to account for their resistance, ensuring the reading reflects only the bond under test and not the test leads (FAA-H-8083-30, Fundamentals of Electricity and Electronics).
ACS code: AM.I.A
Correct answer: a low-reading ohmmeter.
Rationale: A continuity check confirms a cable forms an unbroken path of very low resistance, so a low-reading ohmmeter is the correct instrument: it shows near-zero ohms for a sound conductor and infinity for a break. A high-voltage (insulation) tester checks insulation, and a series ammeter measures current flow rather than continuity (FAA-H-8083-30, Fundamentals of Electricity and Electronics).
ACS code: AM.I.A
Correct answer: 0.5.
Rationale: Per FAA-H-8083-30, power factor equals true power divided by apparent power. Apparent power is voltage times current: 400 V × 20 A = 8,000 VA (8 kVA). The true power is 4 kW, so the power factor is 4 ÷ 8 = 0.5.
ACS code: AM.I.A
Correct answer: in series with the circuit.
Rationale: Per FAA-H-8083-30, an ammeter must carry the same current it is measuring, so it is connected in series with the circuit. Its very low internal resistance keeps the disturbance small. Connecting it in parallel would place its low resistance across the supply and effectively cause a short circuit.
ACS code: AM.I.A
Correct answer: 1999.
Rationale: Per FAA-H-8083-30, a 3 1/2-digit display has three full digits (0 through 9) plus a leading half digit limited to 0 or 1, so the maximum count is 1999. A full four-digit count would reach 9999, and 999 corresponds to only three full digits.
ACS code: AM.I.A
Correct answer: infinite resistance.
Rationale: Per FAA-H-8083-30, an open circuit provides no complete path for current, so its resistance is effectively infinite. An ohmmeter therefore indicates infinity (or an over-range indication). A zero or mid-scale reading would instead indicate a complete path of low or moderate resistance.
ACS code: AM.I.A
Correct answer: The ohmmeter (resistance) function.
Rationale: Per FAA-H-8083-30, the ohmmeter function must drive a known current through the unknown resistance and measure the result, so it requires an internal battery. The voltmeter and ammeter functions take their energy from the circuit under test, which is why a dead battery affects only the resistance ranges of a multimeter.
ACS code: AM.I.A
Correct answer: Black.
Rationale: Per FAA-H-8083-30, by convention the black lead is the negative or common lead and plugs into the COM socket, while the red lead is positive and goes to the volts/ohms/amps socket. Observing this color coding keeps polarity correct on DC ranges and during resistance measurement.
ACS code: AM.I.A
Correct answer: parallel with the component.
Rationale: Voltage is the difference in potential between two points, so a voltmeter is connected in parallel (across) the component to sample the drop without breaking the circuit. The high-impedance voltmeter draws negligible current. Connecting it in series, as is done for current with an ammeter, would not measure the drop and would interrupt the circuit.
ACS code: AM.I.A
Correct answer: bridge rectifier circuit.
Rationale: A moving-coil (D'Arsonval) movement responds only to direct current, so to read alternating current the meter first passes the AC through a bridge rectifier, converting it to a unidirectional current the coil can deflect. The scale is then calibrated to show the equivalent AC value. A plain moving-coil or moving-iron element alone does not provide this AC capability.
ACS code: AM.I.A
Correct answer: Measure the millivolt drop across the connection with a millivoltmeter.
Rationale: A high-resistance joint is found by passing the normal circuit current and measuring the small voltage (millivolt) drop across the connection while it is live, since a poor crimp drops more voltage for the same current. An ohmmeter must not be used on a live circuit, and a high-voltage insulation (megohm) test checks insulation rather than joint resistance.
ACS code: AM.I.A
Correct answer: A time domain reflectometer.
Rationale: A time domain reflectometer sends a pulse down the line and times the reflections from any open or short, both detecting and locating the fault along the run. A plain ohmmeter shows only end-to-end resistance and cannot pinpoint where along the cable a discontinuity lies.
ACS code: AM.I.A
Correct answer: multimeter set to AC volts.
Rationale: An open circuit in a live AC supply is checked with a multimeter set to AC volts: voltage appears across the break but is absent across a sound conductor, so the meter reads supply voltage where the circuit is open. An ohmmeter must never be used on a live circuit, and an ammeter reads only the current that would flow if the circuit were complete.
ACS code: AM.I.A
Correct answer: voltmeter.
Rationale: A multiplier is a high-value resistor placed in series with a meter movement to extend its voltage range, dropping the excess voltage so only a small fraction appears across the movement. By contrast, an ammeter's range is extended with a parallel shunt, so the multiplier specifically belongs to the voltmeter.
ACS code: AM.I.A
Correct answer: average value of the waveform.
Rationale: A typical AC voltmeter uses a moving-coil movement behind a rectifier, so its deflection responds to the average (mean) value of the rectified waveform, with the scale calibrated to read RMS. It does not directly sense peak or peak-to-peak voltage, which is why the average value is the quantity the instrument inherently measures.
ACS code: AM.I.A
Correct answer: check the specific gravity of battery electrolyte.
Rationale: A hydrometer draws up battery electrolyte and floats a calibrated bulb to read its specific gravity, which indicates the cell's state of charge as acid concentration changes with charge and discharge. Specific gravity, not a vague density level or air humidity, is the property the float is calibrated to measure.
ACS code: AM.I.A
Correct answer: thermometer used to measure high temperatures.
Rationale: A pyrometer is an instrument used to measure high temperatures, such as cylinder head temperature or turbine exhaust gas temperature, that are beyond the range of an ordinary thermometer. It commonly uses a thermocouple that produces a voltage proportional to temperature, which is read on a calibrated meter.
ACS code: AM.I.A
Correct answer: take a reading of atmospheric humidity.
Rationale: A hygrometer measures the humidity, or moisture content, of the air. It should not be confused with the similarly named hydrometer, which measures the specific gravity of a liquid such as battery electrolyte.
ACS code: AM.I.A
Correct answer: is rectified, and the meter indicates the average value.
Rationale: A moving-coil movement responds only to direct current, so alternating current must first be rectified. The pointer then deflects in proportion to the average (mean) value of the rectified waveform, and the scale is calibrated to read that value.
ACS code: AM.I.A
Correct answer: connect a low-value shunt resistor in parallel with the movement.
Rationale: To increase the current range of an ammeter, a low-value shunt resistor is connected in parallel with the meter movement so the excess current bypasses the movement and only full-scale current flows through it. A series multiplier resistor is used to extend a voltmeter range, not a current range.
ACS code: AM.I.A
Correct answer: high.
Rationale: A voltmeter is connected in parallel across the component being measured, so it must have a very high internal resistance to draw negligible current and avoid loading the circuit or disturbing the voltage being read.
ACS code: AM.I.A
Correct answer: low.
Rationale: An ammeter is connected in series so all the circuit current flows through it. Its internal resistance must be very low to minimize the voltage drop it introduces and to avoid altering the current it is intended to measure.
ACS code: AM.I.A
Correct answer: cramped at the high-resistance end.
Rationale: An ohmmeter scale is non-linear and reversed: zero ohms produces full deflection, and the scale crowds together toward the high-resistance (low-current) end. As a result, high resistance values are read with less precision because the scale is cramped at the high-resistance end.
ACS code: AM.I.A
Correct answer: a low-reading ohmmeter.
Rationale: A continuity test checks for a complete, low-resistance path, so a low-reading ohmmeter is used to confirm near-zero resistance through the conductor. An ammeter measures current flow rather than path integrity, and a high-voltage insulation tester is used for a different purpose.
ACS code: AM.I.A
Correct answer: a current-carrying coil pivoted in a permanent-magnet field.
Rationale: In a permanent-magnet moving-coil movement, the deflecting force comes from current passing through a pivoted coil located in the field of a permanent magnet, producing a torque proportional to the current. The hairsprings provide the opposing restoring torque, not the deflecting force.
ACS code: AM.I.A
Correct answer: controlling force.
Rationale: Per FAA-H-8083-30, the restoring (controlling) force—normally supplied by hairsprings—opposes pointer deflection and returns the pointer to zero when no current flows, while also balancing the deflecting force to give a steady reading. The deflecting force drives the pointer up-scale, so it does not return it to zero.
That is a free sample of the 60 questions tagged to ACS AM.I.A. The rest, the adaptive engine that serves you more of whatever you keep missing, and the timed exam simulator come with a free account.
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