Basic Electrical Practice Tests

Fundamental electrical theory tests covering Ohm's Law, circuits, voltage, current, and resistance.

14 tests · 355 questions · Free · No signup · NEC 2020 · 2023 · 2026
Based on the National Electrical Code (NFPA 70) — NEC 2020, 2023 & 2026 editions covered.  ·  Last reviewed Jun 2026

Start Here — Electrical Theory Fundamentals

These basic electrical tests cover the theory that everything else in electrical work is built on. Before you can understand why the NEC sizes conductors the way it does, or why motors have overcurrent protection rules, you need to understand the fundamentals: what voltage, current, and resistance are, how they relate to each other, and how circuits behave.

This category is ideal for new apprentices, HVAC students, and anyone who wants to build a stronger foundation before moving into NEC code study. The questions are straightforward — no NEC article lookups needed. You either know the concept or you do not.

The Three Core Concepts

Voltage (V)

Voltage is electrical pressure — the force that pushes electrons through a circuit. Measured in volts. Higher voltage means more force pushing current through the same resistance. Household circuits in the US are 120V or 240V. Three-phase commercial power is 208V, 240V, or 480V.

Current (I)

Current is the flow of electrons — how many electrons pass a point per second. Measured in amperes (amps). More current means more electrons flowing. A 20-amp circuit can push 20 amps of current before the breaker trips.

Resistance (R)

Resistance is opposition to current flow. Every conductor has some resistance. High resistance means less current for the same voltage. Resistance is measured in ohms. Short circuits have very low resistance — too much current flows, which is why breakers exist.

Ohm's Law ties these together: V = I × R. Knowing any two values lets you calculate the third. This is the most important equation in electrical theory.

Ohm's Law & Power Series Circuits Parallel Circuits Voltage & Current Resistance & Conductance Electrical Safety
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NEC 2023

DC Generator theory

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Free online DC generator theory practice test. 25 basic electrical questions on generator losses, EMF equation, types of DC generators, armature reaction, commutation, critical field resistance, and generator characteristics. Good for electrician exam prep.

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Transformer Practice Quiz Test-1

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Induction Motor Practice Quiz Questions

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DC Series Motor Practice Test Questions

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DC Shunt Motor Practice Test Questions

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Synchronous Generator Practice Questions

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circuit breaker theory quiz question and answers

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commercial load calculations-2

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Free online commercial load calculation practice test based on the NEC. 25 basic electrical questions on receptacle loads, demand factors, electric ranges, continuous loads, feeder and service sizing. Good for electrician exam prep.

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Electrical fuse Practice test

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Circuit Breaker Practice Test 2

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Free online circuit breaker practice test, part 2. 25 basic electrical questions on MCB, MCCB, ACB, trip mechanisms, protection relays, and switchgear practice. Good for electrician exam prep.

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Ohm's Law Practice Test 1

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Free online Ohm's Law practice test. 25 basic electrical questions on voltage, current, resistance, power calculations, series and parallel circuits, and wire resistance. Good for electrician exam prep.

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Branch circuit Practice Questions

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Free online branch circuit practice test based on the NEC. 25 basic electrical questions on branch circuit ratings, GFCI and AFCI protection, receptacle spacing, and overcurrent protection rules. Good for electrician exam prep.

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Service conductor practice test questions-1

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Free online service conductor practice test based on the NEC. 25 basic electrical questions on service disconnects, service clearances, grounding, and service sizing. Good for electrician exam prep.

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Ohm's Law in Practice

Ohm's Law (V = I × R) has three forms — use whichever you need based on what you know:

FindFormulaExample
Voltage (V)V = I × R2A × 60Ω = 120V
Current (I)I = V ÷ R120V ÷ 60Ω = 2A
Resistance (R)R = V ÷ I120V ÷ 2A = 60Ω

Series vs. Parallel Circuits

Series Circuits

  • Current is the same through every component.
  • Total voltage = sum of voltage drops across each component.
  • Total resistance = sum of all resistances.
  • If one component opens (breaks), the whole circuit stops.

Parallel Circuits

  • Voltage is the same across every branch.
  • Total current = sum of branch currents.
  • Total resistance is less than the smallest branch resistance.
  • If one branch opens, the others keep working.

Power Formula

Power (in watts) tells you how much energy a device uses per second. The formula is P = V × I. A 120V circuit with 10 amps flowing carries 1,200 watts of power. Knowing power helps you size conductors and breakers correctly.

Basic Electrical — FAQ

Do I need to know this stuff for the journeyman exam?

Yes. The journeyman exam tests load calculations (using power and current formulas), motor sizing (using full-load amps), and voltage drop calculations (which combine Ohm's Law with distance and wire size). These all come from basic theory.

What is the difference between AC and DC?

DC (direct current) flows in one direction only — like a battery. AC (alternating current) reverses direction many times per second. In the US, AC runs at 60 Hz (60 cycles per second). Most building power is AC. Batteries, solar panels, and some EV charging circuits use DC.

Why does 240V use less current than 120V for the same power?

From P = V × I: if power (watts) is the same and voltage doubles, current must halve. That is why large appliances like electric dryers, ranges, and HVAC systems run on 240V — lower current means smaller conductors and less heat generated in the wiring.