Why Electronics Information Matters
The Electronics Information (EI) section tests basic knowledge of electrical principles, circuits, and components. EI feeds into some of the most competitive line scores: Army EL (Electronics), GM (General Maintenance), and MM (Mechanical Maintenance); Air Force Electronic (E) composite; and Navy/Marine technical composites like AR+MK+EI+GS.
If you're targeting any electronics, IT, cyber, communications, or avionics job, EI is one of the most important sections to master. The CAT-ASVAB has 16 EI questions; the paper version has 20.
Core Concept 1: Voltage, Current, and Resistance
These three quantities are the foundation of everything in EI:
- Voltage (V) — electrical pressure; measured in volts (V). Think of it as the force pushing electrons.
- Current (I) — flow of electrons; measured in amperes (A). Think of it as how many electrons are flowing.
- Resistance (R) — opposition to current flow; measured in ohms (Ω). Think of it as friction in the wire.
Ohm's Law: V = I × R
Rearrangements: I = V/R and R = V/I. Know how to solve for any one variable given the other two.
Example: A circuit has 12V and 4Ω resistance. What is the current? → I = 12/4 = 3 amps
Core Concept 2: Power
Power (P) — the rate at which electrical energy is used; measured in watts (W).
P = V × I
Combined with Ohm's Law: P = I²R and P = V²/R
Example: A 120V appliance draws 5A. What is its power? → P = 120 × 5 = 600 watts
Core Concept 3: Series vs. Parallel Circuits
This is the most tested concept in the EI section. Know both cold.
Series Circuit
- Components connected end-to-end in a single path
- Current is the same through every component
- Voltage is divided across components proportionally
- Total resistance = sum of all resistances: R_total = R₁ + R₂ + R₃
- If one component fails (burns out), the whole circuit breaks
Parallel Circuit
- Components connected across the same two points (multiple paths)
- Voltage is the same across every component
- Current is divided among the branches
- Total resistance is less than the smallest individual resistor: 1/R_total = 1/R₁ + 1/R₂ + 1/R₃
- If one component fails, others continue to work (like household circuits)
Core Concept 4: Electrical Components
Know what each component does:
- Resistor — limits current flow
- Capacitor — stores electrical charge; charges up, then releases; blocks DC, passes AC
- Inductor (coil) — stores energy in a magnetic field; resists changes in current; passes DC, blocks AC
- Diode — allows current to flow in only one direction (like a one-way valve)
- Transistor — acts as an amplifier or switch
- Transformer — changes AC voltage up (step-up) or down (step-down) using electromagnetic induction
- Fuse / Circuit breaker — protects the circuit by breaking it when current exceeds a safe limit
Core Concept 5: AC vs. DC
- DC (Direct Current) — current flows in one direction. Batteries produce DC.
- AC (Alternating Current) — current reverses direction repeatedly. House outlets (120V, 60 Hz) are AC.
- Frequency (Hz) = number of complete cycles per second. 60 Hz means 60 full cycles per second.
- Transformers only work with AC, not DC.
Core Concept 6: Conductors, Insulators, and Semiconductors
- Conductors — materials that allow current to flow easily (copper, silver, aluminum, gold)
- Insulators — materials that resist current flow (rubber, plastic, glass, ceramic)
- Semiconductors — conduct under some conditions but not others (silicon, germanium). Used in transistors and diodes.
Core Concept 7: Magnetism and Electromagnetism
- Moving electric current creates a magnetic field. This is the principle behind motors and electromagnets.
- A changing magnetic field creates voltage (generator principle — electromagnetic induction).
- Like magnetic poles repel; opposite poles attract.
- An electromagnet can be turned on and off by controlling current flow.
EI Study Strategy
EI rewards memorization and concept understanding — there's less calculation than AR or MK. Study by concept:
- Master Ohm's Law and power calculations first. These appear in almost every practice test.
- Draw series and parallel circuits. Calculate total resistance and current flow in each. Practice until it's automatic.
- Make a component flashcard set. One card per component — name, symbol, and what it does.
- Learn what fails in series vs. parallel. "If one light bulb burns out, do the others stay on?" is a classic question type.
Use the Electronics Information drills to test your knowledge and see explanations for every question.