Overview
The Electronics Information section of the ASVAB tests your knowledge of basic electrical principles, circuit types, electronic components, measurement units, and safety practices. Questions focus on applying formulas, identifying component functions, and understanding how circuits behave under different conditions. Mastering Ohm's Law and circuit analysis will cover a significant portion of the test.
---
Ohm's Law & Power
Core Formulas
The three most essential formulas you must know cold:
| Formula | Solves For | Rearrangement |
|---|---|---|
| I = V ÷ R | Current (Amps) | — |
| V = I × R | Voltage (Volts) | — |
| R = V ÷ I | Resistance (Ohms) | — |
| P = V × I | Power (Watts) | I = P/V or V = P/I |
Key Concepts
• Voltage (V) – The electrical pressure or potential difference that drives current through a circuit, measured in volts (V)
• Current (I) – The flow of electrical charge through a conductor, measured in amperes (amps, A)
• Resistance (R) – Opposition to the flow of current, measured in ohms (Ω)
• Power (P) – The rate at which electrical energy is consumed or produced, measured in watts (W)
Worked Examples
• 12V ÷ 4Ω = 3A (current)
• 2A × 6Ω = 12V (voltage)
• 60W ÷ 120V = 0.5A (current draw of a light bulb)
Key Terms
• Ohm's Law – The relationship between voltage, current, and resistance (V = IR)
• Watt – Unit of power; 1 watt = 1 volt × 1 ampere
• Proportional relationship – Current increases when voltage increases (if R is constant); current decreases when resistance increases (if V is constant)
> ### ⚠️ Watch Out For
> - Always identify which variable you're solving for before choosing a formula
> - If resistance doubles, current is halved — not eliminated. The relationship is inversely proportional
> - Don't confuse power (watts) with energy (watt-hours); they are related but different concepts
> - Remember: P = V × I, not P = V + I — it's multiplication
---
Circuit Types
Series Circuits
• Current is identical at every point in the circuit
• Total resistance = sum of all individual resistors (R_total = R1 + R2 + R3...)
• Voltage is divided among components
• If one component fails, the entire circuit breaks
• Example: 2Ω + 3Ω + 5Ω = 10Ω total
Parallel Circuits
• Voltage is the same across every branch
• Current is divided among branches
• Total resistance is less than the smallest individual resistor
• If one branch fails, other branches continue to operate
• Formula for two resistors in parallel: R_total = (R1 × R2) ÷ (R1 + R2)
Comparison Table
| Property | Series | Parallel |
|---|---|---|
| Current | Same everywhere | Divides among branches |
| Voltage | Divides among components | Same across all branches |
| Total Resistance | Increases with each added resistor | Decreases with each added path |
| Failure Effect | Breaks entire circuit | Only affects that branch |
Key Terms
• Short circuit – An unintended low-resistance path that bypasses the normal load, causing dangerously excessive current flow
• Open circuit – A break in the circuit that stops all current flow
• Load – Any device in a circuit that consumes electrical energy (bulb, motor, resistor)
> ### ⚠️ Watch Out For
> - In series, adding more resistors increases total resistance
> - In parallel, adding more resistors decreases total resistance — this is counterintuitive but critical
> - Don't mix up which property stays constant: current stays the same in series; voltage stays the same in parallel
> - A short circuit does NOT mean no current — it means too much current on an unintended path
---
Electronic Components
Passive Components
• Resistor – Opposes and limits current flow; measured in ohms (Ω)
• Capacitor – Stores electrical energy as an electric field between two conductive plates; measured in farads (F), commonly microfarads (µF) or picofarads (pF)
• Inductor – Stores energy in a magnetic field; opposes changes in current (the opposite of a capacitor, which opposes changes in voltage)
Active/Semiconductor Components
• Diode – Allows current to flow in one direction only; acts as a one-way valve; used in rectifiers to convert AC to DC
• Transistor – Amplifies or switches electronic signals; the fundamental building block of modern electronics and computers
Power Components
• Transformer – Transfers electrical energy between circuits using electromagnetic induction; can step voltage up or down; only works with AC, not DC
• Fuse – A one-time protection device that melts and breaks the circuit when current exceeds a safe level; must be replaced after it blows
• Circuit Breaker – Automatically interrupts excessive current; can be reset after the fault is corrected (unlike a fuse)
Key Terms
• Semiconductor – A material with conductivity between a conductor and insulator (silicon, germanium); the basis for diodes and transistors
• Rectification – Converting AC to DC, typically using diodes
• Electromagnetic induction – The process by which a changing magnetic field produces a voltage (basis for transformers and generators)
• Farad (F) – The unit of capacitance; in practice, most capacitors are measured in µF or pF
> ### ⚠️ Watch Out For
> - A fuse is destroyed when it functions — it must be replaced; a circuit breaker can be reset
> - Transformers only work with AC current, not DC
> - A capacitor stores energy in an electric field; an inductor stores energy in a magnetic field — don't swap these
> - Diodes don't just "reduce" current — they block it entirely in one direction
---
Electrical Measurements & Units
Units Reference Chart
| Quantity | Unit | Symbol | Measuring Instrument |
|---|---|---|---|
| Voltage | Volt | V | Voltmeter (connected in parallel) |
| Current | Ampere | A | Ammeter (connected in series) |
| Resistance | Ohm | Ω | Ohmmeter / Multimeter |
| Power | Watt | W | Wattmeter |
| Capacitance | Farad | F | Capacitance meter |
| Frequency | Hertz | Hz | Frequency counter / Oscilloscope |
AC vs. DC
• DC (Direct Current) – Flows in one constant direction; produced by batteries and DC generators
• AC (Alternating Current) – Periodically reverses direction; produced by power plants; used in US homes
• Frequency – The number of complete AC cycles per second, measured in hertz (Hz)
• US power grid operates at 60 Hz; most of Europe uses 50 Hz
Key Terms
• Multimeter – A versatile instrument that measures voltage, current, and resistance
• Hertz (Hz) – One complete AC cycle per second
• Cycle – One full AC waveform, from zero up to peak, back to zero, down to negative peak, and back to zero
> ### ⚠️ Watch Out For
> - An ammeter must ALWAYS be connected in series — connecting it in parallel can damage it
> - A voltmeter must ALWAYS be connected in parallel — this is the opposite of the ammeter
> - Don't confuse frequency (Hz) with voltage (V) — they are completely different properties of AC
> - The US standard is 120V at 60 Hz for household outlets — memorize this
---
Electrical Safety & Practical Concepts
Protective Devices
• Fuse – Melts to break a circuit; single-use; rated by maximum amperage
• Circuit Breaker – Trips to break a circuit; resettable; rated by maximum amperage
• GFCI (Ground Fault Circuit Interrupter) – Detects small current imbalances and shuts off power instantly; required near water sources
Grounding
• Electrical grounding – Connecting a circuit to the earth to provide a safe discharge path for excess current
• Prevents electric shock and protects equipment from voltage surges
• In US wiring: green or bare copper wire is the ground conductor
US Standard Household Wiring Colors
| Wire Color | Function |
|---|---|
| Black | Hot (live) conductor |
| White | Neutral conductor |
| Green / Bare copper | Ground |
Water and Electricity
• Water (especially with dissolved minerals and salts) is a conductor of electricity
• Creates a direct path for current to flow through a person, causing electrocution
• This is why GFCI outlets are required in bathrooms, kitchens, and outdoor areas
Key Terms
• Ground fault – Unintended current flow to ground, often through a person
• Overcurrent – Current exceeding the safe rated capacity of a wire or device
• Insulator – A material that resists electrical current (rubber, plastic, glass); used to safely contain conductors
> ### ⚠️ Watch Out For
> - A circuit breaker and a fuse do the same job differently — the key difference is that breakers are resettable
> - White = neutral, not ground; green/bare = ground — don't confuse these in wiring questions
> - Grounding does not prevent all shocks — it provides a safer path for fault current
> - Pure distilled water is actually a poor conductor; it's the dissolved minerals that make tap water dangerous
---
Quick Review Checklist
Use this checklist before test day to confirm you know each concept:
• [ ] Ohm's Law: Memorize V = IR and all three rearrangements
• [ ] Power formula: P = V × I and rearrangements (I = P/V, V = P/I)
• [ ] Series circuits: Current is constant; resistance adds up; one failure breaks all
• [ ] Parallel circuits: Voltage is constant; resistance decreases; branches work independently
• [ ] Capacitor stores energy in an electric field (unit: farad)
• [ ] Inductor stores energy in a magnetic field; opposes current changes
• [ ] Diode = one-way current flow only
• [ ] Transistor = amplifies or switches signals
• [ ] Transformer = steps AC voltage up or down; does NOT work with DC
• [ ] Ammeter connects in series; Voltmeter connects in parallel
• [ ] US power: 120V, 60 Hz AC
• [ ] Fuse is destroyed when it blows; circuit breaker can be reset
• [ ] US wiring: Black = hot, White = neutral, Green/bare = ground
• [ ] Water + electricity = dangerous due to dissolved mineral conductivity
• [ ] Doubling resistance halves current (inverse relationship)
• [ ] Adding resistors in parallel always decreases total resistance