35 Electronics Information (EI) Practice Questions & Answers

1. 1. A 9 V battery is connected across a single 45 Ω resistor. How much current flows?

   • A.5 mA
   • B.2 mA
   • C.20 mA
   • D.200 mA✓ Answer

   By Ohm's law I = V/R = 9 V ÷ 45 Ω = 0.2 A, which is 200 mA. The 5 mA figure comes from dividing resistance by voltage (45 ÷ 9), and 20 mA and 2 mA are decimal-place slips when converting amperes to milliamperes.

   Ref QB-46EDH3Source: Official ASVAB subtests, officialasvab.com — Electronics Information (EI): knowledge of electricity and electronics; Ohm's law, I = V/RReport a problem with this question

2. 2. A lamp on a 120 V circuit draws 0.5 A. How much power does it use?

   • A.120 W
   • B.240 W
   • C.60 W✓ Answer
   • D.30 W

   Electric power is P = V × I = 120 V × 0.5 A = 60 W. Dividing voltage by current gives 240 W (that is actually the lamp's resistance in ohms), squaring the current before multiplying gives 30 W, and 120 W comes from treating the voltage as if it were the wattage.

   Ref QB-KN88X2Source: Official ASVAB subtests, officialasvab.com — Electronics Information (EI): knowledge of electricity and electronics; electric power, P = VIReport a problem with this question

3. 3. A 1,500 W space heater runs for 4 hours. How much electrical energy does it use?

   • A.6,000 kWh
   • B.6 kWh✓ Answer
   • C.60 kWh
   • D.375 kWh

   Energy equals power times time: 1.5 kW × 4 h = 6 kWh. Writing 6,000 kWh forgets to convert watts to kilowatts, 375 kWh divides power by time instead of multiplying, and 60 kWh is a decimal-place slip.

   Ref QB-3633C2Source: Official ASVAB subtests, officialasvab.com — Electronics Information (EI): knowledge of electricity and electronics; electrical energy, E = P × t (kilowatt-hours)Report a problem with this question

4. 4. A resistor is marked 4.7 kΩ. What is its resistance in ohms?

   • A.470 Ω
   • B.47,000 Ω
   • C.4,700,000 Ω
   • D.4,700 Ω✓ Answer

   The prefix kilo (k) means 1,000, so 4.7 kΩ = 4.7 × 1,000 = 4,700 Ω. The answers 470 Ω and 47,000 Ω shift the decimal point one place the wrong way, and 4,700,000 Ω treats kilo as if it were mega (one million).

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5. 5. Which of these materials is a semiconductor used to make diodes and transistors?

   • A.Copper
   • B.Graphite
   • C.Mica
   • D.Silicon✓ Answer

   Silicon is the standard semiconductor: its conductivity lies between that of conductors and insulators and can be controlled by doping, which is how diodes and transistors are made. Copper is a conductor, mica is an insulator, and graphite, sometimes wrongly listed as a semiconductor, is a conductor.

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6. 6. In conventional current notation, current in the external circuit is said to flow from:

   • A.The negative terminal to the positive terminal
   • B.The positive terminal to the negative terminal✓ Answer
   • C.The negative terminal out to the ground wire
   • D.The ground wire back to the positive terminal

   Conventional current is defined as flowing from the positive terminal through the external circuit to the negative terminal. Negative to positive describes electron flow, the actual movement of electrons, which is the opposite direction; ground is not the source or destination of current in either convention.

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7. 7. Resistors of 10 Ω, 20 Ω and 70 Ω are connected in series. What is the total resistance?

   • A.70 Ω
   • B.100 Ω✓ Answer
   • C.6 Ω
   • D.33 Ω

   In a series circuit the resistances simply add: 10 + 20 + 70 = 100 Ω. The answer 33 Ω averages the three values, about 6 Ω is what you get by wrongly combining them as if they were in parallel, and 70 Ω takes only the largest resistor.

   Ref QB-56SQP4Source: Official ASVAB subtests, officialasvab.com — Electronics Information (EI): knowledge of electricity and electronics; series resistance, Rt = R1 + R2 + R3Report a problem with this question

8. 8. Two 12 Ω resistors are connected in parallel. What is their equivalent resistance?

   • A.144 Ω
   • B.24 Ω
   • C.6 Ω✓ Answer
   • D.12 Ω

   For n equal resistors in parallel, Rt = R/n, so 12 Ω ÷ 2 = 6 Ω; the product-over-sum rule gives the same result (144 ÷ 24). Adding them as if in series gives 24 Ω, assuming the total equals one branch gives 12 Ω, and 144 Ω multiplies without dividing by the sum.

   Ref QB-GN68EXSource: Official ASVAB subtests, officialasvab.com — Electronics Information (EI): knowledge of electricity and electronics; parallel resistance, Rt = R1R2/(R1 + R2)Report a problem with this question

9. 9. Two resistors are connected in parallel across a battery. A third resistor is then added in parallel with them. What happens?

   • A.Total resistance falls and the battery supplies more current✓ Answer
   • B.Total resistance stays the same but each branch gets less voltage
   • C.Total resistance rises and the battery supplies less current
   • D.Total resistance rises but the battery current stays the same

   Each new parallel branch gives current another path, so the equivalent resistance drops below the smallest branch and, with the same battery voltage, total current rises. Every parallel branch still has the full battery voltage across it, so branch voltage does not fall.

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10. 10. Three lamps are wired in series to a battery. The filament in one lamp breaks. What happens to the other two lamps?

    • A.Both stay lit and glow brighter than they did before
    • B.One goes dark and the lamp past the break stays lit
    • C.Both go dark because the single current path is broken✓ Answer
    • D.Both stay lit at the same brightness as before

    A series circuit has only one path, so an open anywhere stops current everywhere and every lamp goes out. Lamps staying lit at the same or greater brightness describes a parallel circuit, and distance from the break makes no difference in a series loop.

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11. 11. Two identical 1.5 V cells are connected in parallel, positive to positive and negative to negative. What does the pair supply?

    • A.3.0 V, with the same capacity as a single cell
    • B.1.5 V, with about half the capacity of one cell
    • C.3.0 V, with about twice the capacity of one cell
    • D.1.5 V, with about twice the capacity of one cell✓ Answer

    Cells in parallel keep the voltage of one cell (1.5 V) but share the load, so together they can deliver roughly twice the charge of one cell. Adding voltages to 3.0 V is the rule for cells in series, which does not increase capacity.

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12. 12. What is the frequency of standard household AC power in the United States?

    • A.60 Hz✓ Answer
    • B.120 Hz
    • C.240 Hz
    • D.50 Hz

    U.S. mains power alternates 60 times per second, so its frequency is 60 Hz. The figure 50 Hz is used in Europe and much of Asia, while 120 and 240 are U.S. household voltages mistakenly given in hertz.

    Ref QB-SAM46KSource: Official ASVAB subtests, officialasvab.com — Electronics Information (EI): knowledge of electricity and electronics; alternating current; U.S. residential 120 V / 60 HzReport a problem with this question

13. 13. A transformer's primary coil has 100 turns and is connected to 120 V AC. Its secondary coil has 400 turns. What is the secondary voltage?

    • A.30 V
    • B.120 V
    • C.480 V✓ Answer
    • D.4 V

    The voltage ratio equals the turns ratio, Vs/Vp = Ns/Np, so Vs = 120 V × 400/100 = 480 V; more secondary turns make this a step-up transformer. Inverting the ratio gives 30 V, assuming a transformer never changes voltage gives 120 V, and 4 V mistakes the 4:1 turns ratio itself for the output voltage.

    Ref QB-ATS9RKSource: Official ASVAB subtests, officialasvab.com — Electronics Information (EI): knowledge of electricity and electronics; transformer turns ratio, Vs/Vp = Ns/NpReport a problem with this question

14. 14. A transformer is connected to a steady DC battery instead of an AC source. Why does almost no voltage appear at the secondary?

    • A.Steady DC overheats the secondary winding before any voltage can appear
    • B.Steady DC makes an unchanging magnetic field, which induces no voltage✓ Answer
    • C.Steady DC flows only through the iron core and never reaches the windings
    • D.Steady DC is too low in voltage to jump the gap between the two windings

    A transformer works by mutual induction: only a changing magnetic flux induces voltage in the secondary (Faraday's law). Steady DC produces a constant field after the first instant, so nothing is induced. Energy is never meant to jump a gap or travel through the core as current.

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15. 15. A generator produces electricity mainly by:

    • A.Heating a junction of two different metals so a small voltage builds up
    • B.Storing charge on two metal plates so it can be released all at once
    • C.Passing current through coils of wire so a magnetic field turns a shaft
    • D.Rotating coils of wire through a magnetic field so voltage is induced in them✓ Answer

    A generator uses electromagnetic induction: moving a conductor through a magnetic field (or the field past the conductor) induces a voltage. Current making a field that turns a shaft is how a motor works, heating a metal junction describes a thermocouple, and storing charge on plates describes a capacitor.

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16. 16. An electromagnet is made by wrapping insulated wire around an iron nail and connecting a battery. Which change makes it stronger?

    • A.Wrapping more turns of wire around the same nail✓ Answer
    • B.Adding a resistor in series to reduce the coil current
    • C.Replacing the iron nail with a wooden dowel of equal size
    • D.Reversing the battery so current flows the other way

    An electromagnet's strength grows with the number of turns and the current through them, and an iron core concentrates the field. Removing the iron core or lowering the current weakens it, and reversing the battery only swaps the north and south poles without changing strength.

    Ref QB-QAWETGSource: Official ASVAB subtests, officialasvab.com — Electronics Information (EI): knowledge of electricity and electronics; electromagnetism: field of a current-carrying coilReport a problem with this question

17. 17. Which component stores energy in a magnetic field and opposes changes in current?

    • A.Resistor
    • B.Inductor✓ Answer
    • C.Capacitor
    • D.Diode

    An inductor (coil) builds a magnetic field when current flows and resists any change in that current; its unit is the henry. A capacitor stores energy in an electric field, a resistor turns energy into heat rather than storing it, and a diode controls the direction of current.

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18. 18. A resistor has the color bands brown, black, red, gold, read from left to right. What is its value?

    • A.10000 Ω ±5%
    • B.1000 Ω ±5%✓ Answer
    • C.1000 Ω ±10%
    • D.102 Ω ±5%

    Brown = 1 and black = 0 give the digits 10; the third band, red = 2, is a multiplier of 10², so 10 × 100 = 1000 Ω; gold means ±5%. Reading red as a third digit gives 102 Ω, gold is wrongly taken as 10% (that is silver), and 10000 Ω adds one zero too many.

    Ref QB-PAJ4NFSource: Official ASVAB subtests, officialasvab.com — Electronics Information (EI): knowledge of electricity and electronics; standard resistor color code (EIA/IEC 60062)Report a problem with this question

19. 19. What does a diode do in a circuit?

    • A.Lets current flow in one direction and blocks it in the other✓ Answer
    • B.Stores charge and releases it when the supply voltage drops
    • C.Limits current to a fixed value in both directions equally
    • D.Raises or lowers an AC voltage using two coils of wire

    A diode conducts when forward-biased (anode positive relative to cathode) and blocks current when reverse-biased, which is why it is used in rectifiers. Storing and releasing charge is a capacitor's job, changing AC voltage with two coils is a transformer's, and a resistor, not a diode, opposes current equally in both directions.

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20. 20. A capacitor is connected in series between a signal source and a speaker. How does it treat steady DC and AC?

    • A.It blocks both DC and AC since its plates never touch
    • B.It blocks steady DC but lets AC signals pass✓ Answer
    • C.It passes DC and AC equally once fully charged
    • D.It passes steady DC but blocks AC signals

    Once charged, a capacitor allows no steady DC through its insulating gap, but an alternating voltage keeps charging and discharging it, so AC signals pass. Passing DC while blocking AC describes an inductor; although the plates never touch, AC still gets through by repeated charging.

    Ref QB-N69WS3Source: Official ASVAB subtests, officialasvab.com — Electronics Information (EI): knowledge of electricity and electronics; capacitors: blocking DC, passing ACReport a problem with this question

21. 21. Which copper wire size can safely carry the most current?

    • A.22 AWG
    • B.14 AWG
    • C.18 AWG
    • D.10 AWG✓ Answer

    In the American Wire Gauge system a lower number means a thicker wire, which has less resistance and a higher ampacity, so 10 AWG carries the most current of these. Choosing 22 AWG reverses the scale, the most common gauge mistake.

    Ref QB-5P3R73Source: Official ASVAB subtests, officialasvab.com — Electronics Information (EI): knowledge of electricity and electronics; American Wire Gauge (AWG) sizing and ampacityReport a problem with this question

22. 22. A small current into a transistor's base controls a much larger current between its collector and emitter. This lets a transistor work as:

    • A.An amplifier or an electronic switch✓ Answer
    • B.A storage cell or a backup battery
    • C.A rectifier or a voltage step-up coil
    • D.A fuse or an overcurrent protector

    Because a small base current controls a larger collector current, a transistor can amplify a signal (gain) or, driven fully on or off, act as a switch. Rectifying is a diode's job, stepping up voltage is a transformer's, overcurrent protection is a fuse's, and a transistor stores no energy.

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23. 23. What is a switch whose contacts are opened and closed by an electromagnet called?

    • A.Capacitor
    • B.Relay✓ Answer
    • C.Rheostat
    • D.Rectifier

    A relay uses a small current through a coil to magnetize a core that pulls the switch contacts, letting a low-power circuit control a high-power one. A rheostat is a variable resistor, a rectifier converts AC to DC, and a capacitor stores charge.

    Ref QB-4PQD22Source: Official ASVAB subtests, officialasvab.com — Electronics Information (EI): knowledge of electricity and electronics; relays: electromagnetically operated switchesReport a problem with this question

24. 24. In circuit schematics, a zigzag line drawn in a wire is the symbol for:

    • A.Fuse
    • B.Inductor
    • C.Resistor✓ Answer
    • D.Capacitor

    The zigzag is the standard U.S. symbol for a resistor. An inductor is drawn as a series of loops or coils, a capacitor as two parallel plates, and a fuse as a small rectangle with a line through it or as an S-shaped curve.

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25. 25. In the schematic symbol for a single cell, a longer line and a shorter line are drawn side by side. The longer line marks the:

    • A.Positive terminal✓ Answer
    • B.Ground connection
    • C.Negative terminal
    • D.Internal fuse

    By convention the long plate of a cell symbol is the positive terminal and the short plate is the negative terminal. Ground has its own symbol of stacked, shrinking lines, and a cell symbol does not show any fuse.

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26. 26. A two-input AND gate receives a 1 on one input and a 0 on the other. What is its output?

    • A.1, since an AND gate inverts the input at 0
    • B.0.5, since an AND gate averages its inputs
    • C.0, since an AND gate needs every input at 1✓ Answer
    • D.1, since an AND gate needs one input at 1

    An AND gate outputs 1 only when all of its inputs are 1, so one 0 forces the output to 0. Outputting 1 when any input is 1 describes an OR gate, inverting describes a NOT gate, and digital gates output only 0 or 1, never an average.

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27. 27. To measure the current through a flashlight bulb with an ammeter, how should the meter be connected?

    • A.In parallel across the bulb, so it reads the bulb's current directly
    • B.In series with the bulb, so the bulb's current passes through the meter✓ Answer
    • C.Connected to only one bulb terminal, so no closed path is needed
    • D.In parallel across the battery, so it reads the total supply current

    An ammeter has very low internal resistance and must be placed in series so the current being measured flows through it. Connecting it in parallel across the bulb or across the battery creates a near short circuit that can blow the meter's fuse or damage the battery.

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28. 28. Before using an ohmmeter to measure a resistor that is in a circuit, what should a technician do?

    • A.Turn off and disconnect circuit power, since the meter supplies its own current✓ Answer
    • B.Connect the meter in series with the powered resistor, as with an ammeter
    • C.Set the meter to its highest current range, since resistance is read in amperes
    • D.Leave circuit power on, since the meter needs that current to take a reading

    An ohmmeter measures resistance by sending a small current from its own internal battery, so the circuit must be de-energized; outside voltage gives false readings and can damage the meter. Resistance is read in ohms, not amperes, and the ohmmeter is placed across the component, not in series like an ammeter.

    Ref QB-NXS75SSource: Official ASVAB subtests, officialasvab.com — Electronics Information (EI): knowledge of electricity and electronics; ohmmeter use on de-energized circuitsReport a problem with this question

29. 29. A voltmeter is connected in parallel across a component. Why does a good voltmeter have very high internal resistance?

    • A.So it can send its own test current through the component
    • B.So it lowers the voltage reaching the part being measured
    • C.So it can carry the full circuit current without overheating
    • D.So it draws almost no current and barely changes the circuit✓ Answer

    Because a voltmeter sits in parallel, any current it draws is taken from the circuit; a very high internal resistance keeps that current tiny, so the reading reflects the real circuit. Carrying full circuit current is an ammeter's role, and sending a test current is what an ohmmeter does.

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30. 30. A fuse in a 15 A household circuit keeps blowing. What is the correct response?

    • A.Bridge the fuse holder with wire until the fault is found
    • B.Fit a 10 A fuse so it will blow sooner and protect more
    • C.Find and fix the fault, then fit another 15 A fuse✓ Answer
    • D.Fit a 30 A fuse so it can handle the extra current

    A blowing fuse signals a short circuit or overload, so the cause must be found and repaired and the fuse replaced with one of the same rating, matched to the wire. A larger fuse or a wire bridge lets the wiring overheat and can start a fire, and a smaller fuse just blows during normal use without fixing anything.

    Ref QB-PV7DATSource: Official ASVAB subtests, officialasvab.com — Electronics Information (EI): knowledge of electricity and electronics; overcurrent protection: fuse ratings matched to conductor ampacityReport a problem with this question

31. 31. A GFCI (ground-fault circuit interrupter) outlet in a bathroom cuts power when it detects that:

    • A.Voltage at the outlet rises above its normal 120 V level
    • B.Total current on the circuit exceeds the breaker's rating
    • C.An arcing fault is occurring in damaged wiring in the wall
    • D.Current on the hot wire differs from current on the neutral✓ Answer

    A GFCI compares the current going out on the hot wire with the current returning on the neutral; a difference of a few milliamperes means current is leaking to ground, possibly through a person, so it trips to prevent shock. Overcurrent is the breaker's job, and arc faults are detected by an AFCI.

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32. 32. In standard U.S. household wiring, the white insulated wire is normally the:

    • A.Hot conductor
    • B.Bonding jumper
    • C.Neutral conductor✓ Answer
    • D.Grounding conductor

    By U.S. convention white (or gray) insulation identifies the neutral, which carries current back to the panel. Black or red marks a hot conductor, and green or bare copper marks the equipment grounding conductor, which carries current only during a fault.

    Ref QB-QVJQFUSource: Official ASVAB subtests, officialasvab.com — Electronics Information (EI): knowledge of electricity and electronics; U.S. residential wiring color conventionsReport a problem with this question

33. 33. What is the main practical difference between a circuit breaker and a fuse?

    • A.A breaker can be reset after it trips; a fuse must be replaced✓ Answer
    • B.A breaker limits circuit voltage; a fuse limits circuit current
    • C.A breaker guards people from shock; a fuse guards only against fire
    • D.A breaker works only on AC circuits; a fuse works only on DC circuits

    Both devices open a circuit on overcurrent from a short or overload, but a fuse's metal link melts and must be replaced, while a breaker trips mechanically and can be reset. Ordinary breakers do not provide personal shock protection (that is a GFCI), both work on AC and DC, and neither limits voltage.

    Ref QB-4MS822Source: Official ASVAB subtests, officialasvab.com — Electronics Information (EI): knowledge of electricity and electronics; overcurrent protective devices: fuses and circuit breakersReport a problem with this question

34. 34. A phone charger must turn 120 V AC into low-voltage DC. Which stage performs the AC-to-DC conversion?

    • A.Inverter
    • B.Amplifier
    • C.Rectifier✓ Answer
    • D.Oscillator

    A rectifier, built from diodes, lets current through in only one direction and so converts AC to DC. An inverter does the reverse (DC to AC), an oscillator generates a repeating signal, and an amplifier increases a signal's strength.

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35. 35. An electric motor converts:

    • A.Electrical energy into mechanical motion✓ Answer
    • B.Alternating current into direct current
    • C.Mechanical motion into electrical energy
    • D.Electrical energy into stored chemical energy

    In a motor, current through coils sitting in a magnetic field produces a force that turns the shaft, converting electrical energy into mechanical motion. The reverse conversion is a generator, charging a battery stores chemical energy, and AC-to-DC conversion is a rectifier's job.

    Ref QB-5M5K73Source: Official ASVAB subtests, officialasvab.com — Electronics Information (EI): knowledge of electricity and electronics; electric motors: force on a current-carrying conductor in a magnetic fieldReport a problem with this question

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