Technical Subtest

ASVAB Electronics Information (EI)

EI tests your knowledge of electrical circuits, components, and basic electronics. Critical for electronics, avionics, and communications jobs.

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Score use
Used for job qualification
Focus areas
5
Examples in this guide
5
Section overview

What EI measures

Understanding of electrical circuits, current flow, voltage, resistance, and common electronic components and their functions.

What appears on the test

  • Ohm's LawV = IR calculations and applications
  • Circuit TypesSeries vs parallel circuits and their properties
  • ComponentsResistors, capacitors, diodes, transistors
  • AC vs DCAlternating vs direct current differences
  • Electrical SafetyGrounding, fuses, insulation
Concept visual

Apply Kirchhoff’s circuit laws

Electrical node and loop diagrams demonstrating current and voltage relationships
At a node, current entering equals current leaving; around a closed loop, voltage rises and drops balance.

What to study for EI

Electronics Information becomes manageable when you separate quantities, circuit layouts, and component functions. Trace current paths, label known values with units, and use a small set of laws rather than guessing from a diagram.

01

Voltage, current, and resistance

Understand what each electrical quantity represents and relate them with Ohm's law.

View key facts
  • Voltage is electrical potential difference, current is charge flow, and resistance opposes current.
  • Ohm's law is V = IR.
  • Electrical power can be calculated with P = VI.
02

Series and parallel circuits

Identify which quantities stay the same and which combine in each circuit arrangement.

View key facts
  • Series components share the same current and their resistances add.
  • Parallel branches share the same voltage.
  • Adding a parallel branch lowers equivalent resistance and increases total current for a fixed voltage.
03

Components and semiconductors

Know the basic purpose of resistors, capacitors, inductors, diodes, and transistors.

View key facts
  • A capacitor stores energy in an electric field; an inductor stores energy in a magnetic field.
  • A diode primarily allows current in one direction.
  • A transistor can act as a switch or amplifier.
04

AC, magnetism, and transformers

Connect changing current and magnetic fields to motors, generators, and transformers.

View key facts
  • Direct current flows in one direction; alternating current reverses periodically.
  • A transformer requires changing magnetic flux and therefore operates with AC or varying current.
  • A step-up transformer increases voltage while ideally decreasing current.
05

Meters and electrical safety

Match the measurement to correct meter placement and recognize basic circuit protection.

View key facts
  • An ammeter goes in series; a voltmeter goes in parallel.
  • Measure resistance only on a de-energized circuit.
  • Fuses and circuit breakers open a circuit when current becomes unsafe.

5 ASVAB-style practice questions

Open a question to review the choices, correct answer, and a short explanation.

Q1A circuit has 24 volts across a resistance and carries 6 amperes. What is the resistance?View question and answer
  1. 6 ohms
  2. 4 ohms
  3. 18 ohms
  4. 144 ohms
Correct answerB. 4 ohms

Why: Using R = V ÷ I, resistance = 24 ÷ 6 = 4 ohms.

Q2In a parallel circuit, the voltage across each branch is:View question and answer
  1. Always zero
  2. Added to the other branch voltages
  3. The same as the source voltage
  4. Inversely proportional to wire length only
Correct answerC. The same as the source voltage

Why: Every parallel branch connects across the same two nodes, so each branch has the source voltage across it.

Q3Which component is designed primarily to allow current flow in one direction?View question and answer
  1. Capacitor
  2. Fuse
  3. Transformer
  4. Diode
Correct answerD. Diode

Why: A diode conducts readily when forward biased and blocks most current when reverse biased.

Q4An ideal step-up transformer increases voltage and:View question and answer
  1. Decreases current
  2. Increases current by the same ratio
  3. Leaves current unchanged
  4. Changes the AC output to DC
Correct answerA. Decreases current

Why: With power approximately conserved in an ideal transformer, an increase in voltage corresponds to a decrease in current.

Q5To measure current through a resistor, an ammeter should be connected:View question and answer
  1. In parallel across the power source
  2. In series with the resistor
  3. Across an open switch only
  4. Without opening the circuit path
Correct answerB. In series with the resistor

Why: An ammeter must be placed in series so the current being measured flows through the meter.

EI study strategy

  1. Write V = IR and P = VI from memory before practice.
  2. Mark series paths and parallel nodes directly on circuit diagrams.
  3. Learn every common component by symbol and function.
  4. Include units in calculations to distinguish volts, amperes, ohms, and watts.
  5. Use meter-safety rules as part of the concept, not as separate trivia.
Optional 7-day study planUse this only if you want a day-by-day way to organize the same core topics.Open the full plan
  1. Day 1

    Electrical quantities: Learn charge, current, voltage, resistance, power, and their units.

  2. Day 2

    Ohm's law: Solve for V, I, and R and combine Ohm's law with power.

  3. Day 3

    Circuit layouts: Compare series, parallel, and series-parallel behavior.

  4. Day 4

    Components: Study resistors, capacitors, inductors, diodes, transistors, switches, and protection.

  5. Day 5

    AC and magnetism: Review frequency, transformers, motors, generators, and electromagnetic induction.

  6. Day 6

    Meters and diagrams: Practice symbols, meter placement, and reading simple schematics.

  7. Day 7

    Timed set: Complete 15 mixed questions in 10 minutes and explain every missed circuit.

Ready to practice EI?

Start a free trial to practice Electronics Information and review misses by topic.

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