ASVAB Electronics Information Practice Test

25 practice questions

Choose an answer, then check it under Show answer.

1. Question 1 of 25Hard

   If the diameter of a cylindrical copper wire is doubled while its length remains the same, its electrical resistance will:

   1. AA. decrease to one-fourth of its original value
   2. BB. increase to twice its original value
   3. CC. decrease to one-half of its original value
   4. DD. increase to four times its original value
   Show answer to question 1

   Answer: A. decrease to one-fourth of its original value

   Resistance is inversely proportional to the cross-sectional area of a conductor, which depends on the square of the diameter. Doubling the diameter increases the area by a factor of four, which reduces the electrical resistance to one-fourth of what it was originally.

2. Question 2 of 25Hard

   An aircraft electrical system uses alternating current with a frequency of 400 hertz. What is the time duration of a single cycle in this system?

   1. AA. 0.0400 seconds
   2. BB. 0.0250 seconds
   3. CC. 0.2500 seconds
   4. DD. 0.0025 seconds
   Show answer to question 2

   Answer: D. 0.0025 seconds

   The period of an alternating current wave is found by dividing 1 by the frequency, which yields 1 divided by 400, or 0.0025 seconds. Distractors like 0.0250 seconds represent common decimal-shift errors when converting fractions to decimals.

3. Question 3 of 25Easy

   What is the primary function of a standard 555 timer integrated circuit?

   1. AA. To store large amounts of digital binary program data
   2. BB. To step down alternating current voltage levels efficiently
   3. CC. To produce accurate time delays or continuous electrical pulses
   4. DD. To convert high-voltage alternating current into direct current
   Show answer to question 3

   Answer: C. To produce accurate time delays or continuous electrical pulses

   The 555 timer is widely used in electronic circuits to generate accurate timing delays, pulse trains, and stable oscillations. A rectifier or power supply converts AC to DC, which is not the role of a timer chip.

4. Question 4 of 25Hard

   What component is commonly placed across a DC solenoid coil to protect driver circuits from high-voltage spikes when current is switched off?

   1. AA. A variable rheostat adjusted for low resistance
   2. BB. A step-down transformer connected in series
   3. CC. A ceramic fuse rated for high current surges
   4. DD. A flyback diode connected in reverse bias
   Show answer to question 4

   Answer: D. A flyback diode connected in reverse bias

   When current to an inductive coil is abruptly interrupted, the collapsing magnetic field creates a high-voltage back-EMF spike, which a reverse-biased flyback diode safely dissipates by providing a recirculating path. A ceramic fuse is designed to open during sustained overcurrent faults and cannot suppress rapid inductive voltage spikes.

5. Question 5 of 25Medium

   A step-down transformer has a primary-to-secondary turns ratio of 5:1. If an alternating potential of 240 volts is supplied to the primary winding, what voltage appears across the secondary winding?

   1. AA. 48 volts AC
   2. BB. 1,200 volts AC
   3. CC. 120 volts AC
   4. DD. 24 volts AC
   Show answer to question 5

   Answer: A. 48 volts AC

   A 5:1 primary-to-secondary ratio indicates that the secondary voltage will be one-fifth of the primary voltage. Dividing 240 volts AC by 5 yields 48 volts AC. Multiplying by 5 to obtain 1,200 volts AC is incorrect because that represents a 1:5 step-up transformer rather than a 5:1 step-down transformer.

6. Question 6 of 25Easy

   What is the process of combining an information signal, such as voice or music, with a high-frequency carrier wave called?

   1. AA. Rectification
   2. BB. Amplification
   3. CC. Modulation
   4. DD. Attenuation
   Show answer to question 6

   Answer: C. Modulation

   Modulation is the technique of superimposing an information-bearing signal onto a high-frequency carrier wave for transmission. Amplification increases the overall strength or voltage of an existing signal, but it does not combine information onto a carrier wave.

7. Question 7 of 25Easy

   How does an increase in operating temperature affect the electrical resistance of standard metallic conductors like copper and aluminum?

   1. AA. The resistance increases.
   2. BB. The resistance decreases.
   3. CC. The resistance drops to zero.
   4. DD. The resistance stays the same.
   Show answer to question 7

   Answer: A. The resistance increases.

   Most pure metals have a positive temperature coefficient of resistance, meaning their resistance increases as temperature rises because thermal vibrations impede electron flow. A decrease in resistance typically occurs in semiconductors and negative temperature coefficient thermistors, not ordinary metallic wires.

8. Question 8 of 25Easy

   How many electrical terminals does a standard potentiometer typically have?

   1. AA. Three
   2. BB. Two
   3. CC. One
   4. DD. Four
   Show answer to question 8

   Answer: A. Three

   Standard potentiometers have three terminals: two connected to the opposite ends of a resistive track and a third connected to an adjustable wiper contact. A two-terminal device used to adjust resistance is typically classified as a rheostat.

9. Question 9 of 25Medium

   In the standard diode symbol, a triangle points to a straight line. What does this symbol indicate about conventional current?

   1. AA. It flows in either direction equally
   2. BB. It flows only when the diode is reverse biased
   3. CC. It flows from the line side toward the triangle
   4. DD. It flows from the triangle side toward the line
   Show answer to question 9

   Answer: D. It flows from the triangle side toward the line

   The triangle points in the direction of conventional current flow, so current goes from the triangle side, the anode, toward the straight line, the cathode. The line side is the cathode, and a diode does not conduct equally in both directions.

10. Question 10 of 25Medium

    A rectangular pulse wave remains at its positive high state for 3 milliseconds and at zero volts for 7 milliseconds before repeating. What is the duty cycle of this waveform?

    1. AA. 30 percent
    2. BB. 100 percent
    3. CC. 43 percent
    4. DD. 70 percent
    Show answer to question 10

    Answer: A. 30 percent

    Duty cycle is the ratio of pulse active time to the total period, expressed as a percentage. The total period is 3 milliseconds plus 7 milliseconds, which equals 10 milliseconds, making the duty cycle 3 divided by 10, or 30 percent. Seventy percent incorrectly calculates the percentage of time the waveform is off.

11. Question 11 of 25Medium

    When testing a healthy silicon diode with a digital multimeter set to diode-check mode, what should the display show when the meter leads place the diode in reverse bias?

    1. AA. A zero-ohm resistance reading
    2. BB. An open-circuit or out-of-limits reading (OL)
    3. CC. A negative voltage value indicating active current generation
    4. DD. A steady forward voltage drop of roughly 0.7 volts
    Show answer to question 11

    Answer: B. An open-circuit or out-of-limits reading (OL)

    In reverse bias, a functional diode blocks current, prompting a multimeter in diode mode to display an over-limit or open-circuit reading (often shown as 'OL' or '1'). A forward voltage drop of approximately 0.7 volts occurs only during forward bias, while a reading of zero indicates a shorted component.

12. Question 12 of 25Medium

    What does the outward-pointing arrow on the emitter of an NPN transistor symbol indicate?

    1. AA. Direction of minority carrier drift inside the collector
    2. BB. Direction of electron flow entering the base terminal
    3. CC. Direction of conventional current flowing out of the device
    4. DD. Direction of thermal dissipation away from the junction
    Show answer to question 12

    Answer: C. Direction of conventional current flowing out of the device

    The arrow on an NPN transistor emitter points outward to show the direction of conventional current leaving the device. In contrast, a PNP transistor schematic features an arrow pointing inward toward the base.

13. Question 13 of 25Medium

    Which situation is an overload rather than a short circuit?

    1. AA. Worn insulation lets a hot wire touch the metal frame
    2. BB. Too many appliances on one circuit draw more than its rating
    3. CC. Two bare conductors touch each other inside a cord
    4. DD. A metal tool drops across two terminals and current bypasses the load
    Show answer to question 13

    Answer: B. Too many appliances on one circuit draw more than its rating

    An overload occurs when normal loads together draw more current than the circuit is rated for, as with too many appliances on one circuit. The other situations create unintended low-resistance paths that bypass the load, which are short circuits.

14. Question 14 of 25Medium

    In a common-emitter amplifier circuit, how does the phase of the amplified AC output signal at the collector compare to the input signal at the base?

    1. AA. Shifted behind by 270 degrees
    2. BB. In phase with zero degrees of shift
    3. CC. Inverted by 180 degrees
    4. DD. Shifted ahead by 90 degrees
    Show answer to question 14

    Answer: C. Inverted by 180 degrees

    The common-emitter configuration produces an output signal that is inverted, or 180 degrees out of phase, relative to the input signal at the base. A common-collector circuit, also known as an emitter follower, keeps the output in phase with zero degrees of shift but does not provide voltage gain.

15. Question 15 of 25Medium

    To properly measure direct current through an electric motor using a multimeter, how must the test leads be connected to the circuit?

    1. AA. In series with the motor power supply wire
    2. BB. Between the motor frame and earth ground
    3. CC. Across the positive and negative battery terminals
    4. DD. In parallel across the motor terminals
    Show answer to question 15

    Answer: A. In series with the motor power supply wire

    An ammeter must be inserted in series so that all circuit current flows directly through the meter. Connecting an ammeter in parallel across a component or power source creates a low-resistance short circuit that can blow the meter fuse.

16. Question 16 of 25Medium

    A series AC circuit contains 4 ohms of resistance and 3 ohms of inductive reactance. What is the total impedance of the circuit?

    1. AA. 1 ohm
    2. BB. 12 ohms
    3. CC. 7 ohms
    4. DD. 5 ohms
    Show answer to question 16

    Answer: D. 5 ohms

    Impedance in a series circuit is calculated as the vector sum of resistance and reactance, which equals the square root of resistance squared plus reactance squared. Squaring 4 and 3 gives 16 and 9, and the square root of their sum, 25, is 5 ohms. Simply adding the two values directly yields 7 ohms, which is an incorrect algebraic sum that ignores the 90-degree phase difference between resistance and reactance.

17. Question 17 of 25Hard

    An industrial step-down transformer converts an input of 480 volts AC down to 120 volts AC. If the secondary coil has 150 turns, how many turns are wound on the primary coil?

    1. AA. 38 turns
    2. BB. 300 turns
    3. CC. 600 turns
    4. DD. 1,200 turns
    Show answer to question 17

    Answer: C. 600 turns

    The voltage ratio of primary to secondary is 480 divided by 120, which is equal to 4. Because the primary voltage is four times higher than the secondary voltage, the primary coil must have four times as many turns as the secondary coil, meaning 150 multiplied by 4 equals 600 turns. Dividing 150 by 4 to get approximately 38 turns confuses the primary and secondary positions in the ratio.

18. Question 18 of 25Medium

    A 30-volt power supply is connected to a 4-ohm resistor in series with a parallel pair of two 12-ohm resistors. What is the voltage drop across each of the 12-ohm resistors?

    1. AA. 12 volts
    2. BB. 18 volts
    3. CC. 24 volts
    4. DD. 15 volts
    Show answer to question 18

    Answer: B. 18 volts

    The two 12-ohm resistors in parallel have an equivalent resistance of 6 ohms, giving a total circuit resistance of 10 ohms. A 30-volt supply produces 3 amperes of current, creating a 12-volt drop across the 4-ohm series resistor and leaving the remaining 18 volts across the parallel network. The value of 12 volts represents the voltage drop across the series resistor rather than the parallel branch.

19. Question 19 of 25Easy

    What is the standard unit of measurement for electrical inductance?

    1. AA. Tesla
    2. BB. Henry
    3. CC. Ohm
    4. DD. Farad
    Show answer to question 19

    Answer: B. Henry

    The henry is the standard unit of electrical inductance, representing the amount of inductance that produces an electromotive force of one volt when the current changes at one ampere per second. The farad is the unit for electrical capacitance, not inductance.

20. Question 20 of 25Hard

    A 2-ohm, a 3-ohm, and a 6-ohm resistor are connected in parallel. What is the total resistance?

    1. AA. 11 ohms
    2. BB. 3.67 ohms
    3. CC. 1 ohm
    4. DD. 1.5 ohms
    Show answer to question 20

    Answer: C. 1 ohm

    Add the reciprocals: 1/2 plus 1/3 plus 1/6 equals 3/6 plus 2/6 plus 1/6, which is 6/6 or 1. The reciprocal of 1 is 1 ohm. The 11-ohm choice is the series sum, but a parallel total must be less than the smallest resistor.

21. Question 21 of 25Hard

    A 40-volt power source is connected in series with an 8-ohm resistor and a 12-ohm resistor. What is the voltage drop across the 12-ohm resistor?

    1. AA. 16 volts
    2. BB. 24 volts
    3. CC. 20 volts
    4. DD. 40 volts
    Show answer to question 21

    Answer: B. 24 volts

    The total resistance of the series circuit is 8 ohms plus 12 ohms, which equals 20 ohms. The circuit current is 40 volts divided by 20 ohms, or 2 amperes. Multiplying this 2-ampere current by the 12-ohm resistance yields a voltage drop of 24 volts across that resistor. The value of 16 volts is the voltage drop across the 8-ohm resistor, not the 12-ohm resistor.

22. Question 22 of 25Easy

    When two capacitors are connected in parallel in a circuit, what happens to the total capacitance?

    1. AA. It is less than the value of the smallest capacitor.
    2. BB. It equals the sum of the individual capacitances.
    3. CC. It remains equal to the value of the largest capacitor.
    4. DD. It equals the product divided by the sum of the values.
    Show answer to question 22

    Answer: B. It equals the sum of the individual capacitances.

    Connecting capacitors in parallel effectively increases the total plate area, meaning the total capacitance is found by adding the individual capacitances together. The concept of total capacitance being less than the smallest capacitor applies to capacitors connected in series, not parallel.

23. Question 23 of 25Medium

    Two 6-millihenry (mH) inductors are connected in parallel without mutual coupling. What is the total inductance of the circuit?

    1. AA. 12 mH
    2. BB. 36 mH
    3. CC. 6 mH
    4. DD. 3 mH
    Show answer to question 23

    Answer: D. 3 mH

    Inductors in parallel combine like resistors in parallel; two equal parallel components provide half the individual value, yielding 3 mH. Adding the values directly to obtain 12 mH applies to series connections rather than parallel ones.

24. Question 24 of 25Easy

    Approximately how many time constants does it take for an uncharged capacitor in a DC circuit to reach full charge?

    1. AA. 10 time constants
    2. BB. 3 time constants
    3. CC. 1 time constant
    4. DD. 5 time constants
    Show answer to question 24

    Answer: D. 5 time constants

    In practical electronics, a capacitor is considered fully charged after five time constants, at which point it has reached over 99 percent of the supply voltage. After only one time constant, the capacitor has only acquired about 63 percent of the applied voltage.

25. Question 25 of 25Hard

    A hot wire inside a metal tool touches the metal case, and the case is properly grounded. Why does the branch-circuit breaker usually trip?

    1. AA. The neutral wire opens before the hot wire touches the case
    2. BB. The ground wire lowers the tool's normal operating current
    3. CC. A large fault current flows through the ground path
    4. DD. The case becomes a capacitor and discharges slowly
    Show answer to question 25

    Answer: C. A large fault current flows through the ground path

    A grounded metal case gives fault current a low-resistance path, so a large current flows and opens the breaker. The ground connection does not reduce the tool's normal operating current.

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