ASVAB Electronics — Questions and Answers

Question 1: A transformer has a primary winding of 500 turns and a secondary winding of 100 turns. If the primary voltage is 120V, what is the secondary voltage?

24V (Correct answer)
600V
12V
240V

Correct answer: 24V

The turns ratio (500:100 = 5:1) means the secondary voltage is 120V ÷ 5 = 24V.

Question 2: Which type of capacitor is polarized and must be connected with correct polarity in a circuit?

Electrolytic (Correct answer)
Ceramic disc
Mica
Film

Correct answer: Electrolytic

Electrolytic capacitors are polarized due to their construction and will be damaged if connected in reverse polarity.

Question 3: What is the function of a diode in an AC circuit when used as a half-wave rectifier?

Allows current to flow in only one direction (Correct answer)
Amplifies the AC signal
Converts voltage to current
Filters out high frequencies

Correct answer: Allows current to flow in only one direction

A diode passes current in only one direction, so it blocks the negative half-cycle of AC, producing pulsating DC.

Question 4: In a series RLC circuit at resonance, which statement is TRUE?

Impedance is at minimum and equals R (Correct answer)
Impedance is at maximum
Current is at minimum
Capacitive reactance exceeds inductive reactance

Correct answer: Impedance is at minimum and equals R

At resonance, XL equals XC and they cancel, leaving only resistance R as the total impedance.

Question 5: What does a multimeter measure when set to the 'ohms' setting?

Resistance (Correct answer)
Current
Power
Frequency

Correct answer: Resistance

The ohms setting measures electrical resistance; the meter applies a small voltage and measures the resulting current to calculate resistance.

Question 6: Which component is commonly used to regulate voltage in a power supply by maintaining a constant output voltage despite load changes?

Zener diode (Correct answer)
NPN transistor
Inductor
Rheostat

Correct answer: Zener diode

A zener diode is designed to operate in reverse breakdown at a specific voltage, making it ideal for voltage regulation.

Question 7: A circuit draws 3 amps from a 12V battery. What is the power consumed?

36 watts (Correct answer)
4 watts
15 watts
9 watts

Correct answer: 36 watts

Power (P) = Voltage (V) × Current (I) = 12V × 3A = 36 watts.

Question 8: What is the purpose of a bypass capacitor placed across a power supply pin on an integrated circuit?

To filter out high-frequency noise on the supply line (Correct answer)
To increase the supply voltage
To slow down the circuit switching speed
To convert AC to DC

Correct answer: To filter out high-frequency noise on the supply line

Bypass capacitors provide a low-impedance path to ground for high-frequency noise, keeping the supply voltage clean and stable.

Question 9: In a transistor amplifier circuit, what region of operation is the transistor in when it acts as a switch in the 'ON' state?

Saturation (Correct answer)
Cutoff
Active
Breakdown

Correct answer: Saturation

In saturation, both junctions are forward-biased and the transistor conducts maximally, acting like a closed switch.

Question 10: What is the unit of inductance?

Henry (Correct answer)
Farad
Ohm
Tesla

Correct answer: Henry

Inductance is measured in henries (H), named after Joseph Henry who discovered electromagnetic induction independently.

Question 11: Two resistors of 6Ω and 3Ω are connected in parallel. What is the equivalent resistance?

2Ω (Correct answer)
9Ω
4.5Ω
18Ω

Correct answer: 2Ω

For parallel resistors: 1/R = 1/6 + 1/3 = 1/6 + 2/6 = 3/6, so R = 2Ω.

Question 12: Which type of logic gate produces a HIGH output only when ALL inputs are HIGH?

AND gate (Correct answer)
OR gate
NAND gate
NOR gate

Correct answer: AND gate

An AND gate output is HIGH (1) only when every input is HIGH (1); any LOW input forces the output LOW.

Question 13: What happens to the capacitive reactance (XC) of a capacitor as frequency increases?

It decreases (Correct answer)
It increases
It remains constant
It becomes equal to resistance

Correct answer: It decreases

XC = 1/(2πfC), so as frequency (f) increases, XC decreases — capacitors pass high-frequency signals more easily.

Question 14: What is the primary purpose of a heat sink attached to a transistor or voltage regulator?

To dissipate heat and prevent thermal damage (Correct answer)
To increase the gain of the device
To reduce electrical noise
To filter the output signal

Correct answer: To dissipate heat and prevent thermal damage

Heat sinks increase surface area to transfer heat away from the component into the surrounding air, preventing overheating.

Question 15: Which semiconductor device can be used to amplify a signal using three terminals: gate, source, and drain?

MOSFET (Correct answer)
BJT transistor
SCR
DIAC

Correct answer: MOSFET

A MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) uses gate, source, and drain terminals and controls current via an electric field.

Question 16: In a full-wave bridge rectifier, how many diodes are required?

4 (Correct answer)
1
2
6

Correct answer: 4

A bridge rectifier uses 4 diodes arranged in a bridge configuration to convert both half-cycles of AC into DC.

Question 17: What does the term 'gain' mean in the context of an amplifier?

The ratio of output signal amplitude to input signal amplitude (Correct answer)
The maximum voltage the amplifier can handle
The frequency at which the amplifier operates
The power consumed by the amplifier

Correct answer: The ratio of output signal amplitude to input signal amplitude

Gain is the ratio of output to input (voltage, current, or power), indicating how much the amplifier increases the signal.

Question 18: A fuse is rated at 5 amps. If the circuit draws 7 amps, what will happen?

The fuse will blow, opening the circuit (Correct answer)
The fuse will increase its rating automatically
The current will be reduced to 5 amps
Nothing will happen immediately

Correct answer: The fuse will blow, opening the circuit

When current exceeds the fuse rating, the fuse element melts and opens the circuit, protecting the wiring and components.

Question 19: What is the function of an oscilloscope in electronics testing?

To display voltage waveforms as a function of time (Correct answer)
To measure resistance of components
To generate test signals for circuits
To measure the inductance of coils

Correct answer: To display voltage waveforms as a function of time

An oscilloscope displays voltage versus time on a screen, allowing technicians to visualize signal shape, frequency, and amplitude.

Question 20: Which law states that the total current entering a junction equals the total current leaving the junction?

Kirchhoff's Current Law (Correct answer)
Ohm's Law
Faraday's Law
Kirchhoff's Voltage Law

Correct answer: Kirchhoff's Current Law

Kirchhoff's Current Law (KCL) states that charge is conserved at any node, so all currents entering must equal all currents leaving.

Question 21: What is the impedance of a pure inductor at DC (zero frequency)?

Zero (short circuit) (Correct answer)
Infinite (open circuit)
Equal to its inductance value in ohms
Equal to its resistance

Correct answer: Zero (short circuit)

Inductive reactance XL = 2πfL; at DC (f=0), XL = 0, so an ideal inductor is a short circuit to DC.

ASVAB Electronics

A transformer has a primary winding of 500 turns and a secondary winding of 100 turns.
If the primary voltage is 120V, what is the secondary voltage?

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