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BASIC NEC 2023

Conductors, Insulators & Semiconductors Practice Test

Free online conductors, insulators, and semiconductors practice test. 25 basic electrical questions on material properties, copper vs aluminum wiring, resistivity, and semiconductor basics. Good for electrician exam prep.

TOPICS COVERED

Conductor Definition Insulator Definition Semiconductor Definition Common Conductor Materials Copper vs Aluminum Wiring Silver as a Conductor

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Every material falls somewhere on a scale from conductor to insulator. Conductors (copper, aluminum, silver) have free electrons that move easily, letting current flow with little resistance. Insulators (rubber, PVC, glass, porcelain) hold their electrons tightly, blocking current flow. Semiconductors (silicon, germanium) sit in between — their conductivity can be controlled by "doping" them with impurity atoms, which is the basis for diodes, transistors, and every electronic device. Know the practical trade-offs too: copper conducts better than aluminum, but aluminum is lighter and cheaper for large service conductors.

25

Questions

38 min

Time

75%

Pass

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Conductors, Insulators & Semiconductors Practice Test — Question List

Question 1: A material that allows electric current to flow through it easily is called a:

Conductor
Insulator
Capacitor
Resistor

Question 2: A material that strongly resists the flow of electric current is called a:

Insulator
Conductor
Semiconductor
Superconductor

Question 3: A semiconductor is a material whose ability to conduct electricity:

Falls between that of a conductor and an insulator, and can be controlled
Is always a perfect conductor, like silver
Is always a perfect insulator, like glass
Cannot conduct electricity under any condition

Question 4: Which of the following is the most commonly used conductor material in building wiring?

Copper
Rubber
Glass
Porcelain

Question 5: Compared to aluminum, copper is generally preferred for most branch-circuit wiring because copper:

Has higher conductivity and is less prone to connection problems from thermal expansion
Is always cheaper than aluminum
Cannot be used in residential wiring at all
Is a better insulator than aluminum

Question 6: Silver is actually a better electrical conductor than copper, but it is not commonly used for building wiring mainly because of its:

High cost
Poor conductivity
Inability to be drawn into wire
Being classified as an insulator

Question 7: Which of the following is commonly used as an electrical insulator?

Rubber
Copper
Aluminum
Silver

Question 8: Conductivity and resistivity are related in that a material with HIGH conductivity has:

LOW resistivity
HIGH resistivity
Zero resistivity in every case
No relationship at all

Question 9: Resistivity, a property used to compare how strongly different materials oppose current flow, is measured in units of:

Ohm-meters
Watts
Amperes
Volts

Question 10: As the temperature of a typical metal conductor (like copper) increases, its resistance:

Increases
Decreases
Stays exactly the same
Drops to zero

Question 11: As the temperature of a typical semiconductor increases, its resistance:

Decreases — the opposite behavior of a typical metal conductor
Increases, just like a metal conductor
Stays exactly the same as a metal conductor
Becomes infinite

Question 12: Which element is most commonly used to manufacture semiconductor devices such as diodes and transistors?

Silicon
Copper
Rubber
Glass

Question 13: "Doping" a semiconductor material means:

Adding small amounts of impurity atoms to change its electrical conducting properties
Coating the material in rubber insulation
Cooling the material to near absolute zero
Melting the material completely

Question 14: In semiconductor material, an N-type region has an excess of which charge carrier compared to a P-type region?

Free electrons
Protons
Neutrons
Holes (missing electrons)

Question 15: Good electrical conductors, like copper and silver, generally have how many valence electrons in their outer atomic shell?

One
Eight
Zero
Sixteen

Question 16: Electrical insulation on a wire is given a maximum voltage rating because:

Above that voltage, the insulation can break down and allow current to pass through it
Insulation ratings are only cosmetic and have no real effect
Higher-rated insulation always conducts electricity better
The rating only matters for DC circuits, not AC

Question 17: Wire insulation type codes such as THHN and THWN describe the insulation's:

Temperature rating and suitability for wet or dry locations
The exact color the insulation must be
The manufacturer's warranty period
The country the wire was manufactured in

Question 18: "Dielectric strength" of an insulating material describes:

The maximum voltage per unit thickness the material can withstand before it breaks down
How well the material conducts heat
The material's resistance to physical bending
The material's exact melting point

Question 19: When an insulator's dielectric strength is exceeded, the most likely result is:

The insulation breaks down and allows current to pass through where it shouldn't, creating a fault
The insulation becomes a better conductor permanently and safely
Nothing happens — insulation has no voltage limit
The conductor inside instantly turns into an insulator

Question 20: Because aluminum wiring expands and contracts more than copper with temperature changes, aluminum connections require:

Special antioxidant compounds and connectors rated for aluminum to prevent loose, overheating connections
No special connectors — copper connectors work identically
Removing all insulation permanently
Running the wire at double its rated ampacity

Question 21: A superconductor is a special material that, when cooled to extremely low temperatures, exhibits:

Virtually zero electrical resistance
Infinite electrical resistance
Perfect insulating properties
Resistance identical to rubber

Question 22: For the same physical wire size (gauge), copper generally has a higher ampacity than aluminum because copper:

Has lower resistance for the same size, allowing it to carry more current with less heating
Is always physically larger than aluminum wire
Cannot be used outdoors
Has higher resistivity than aluminum

Question 23: The earth (soil) itself can act as a conductor, which is why grounding systems work — but its resistivity:

Varies widely depending on moisture content, soil type, and temperature
Is always exactly zero everywhere
Is always exactly the same everywhere on Earth
Has no effect on grounding system performance

Question 24: Diodes and transistors, common building blocks of electronic circuits, are made from:

Semiconductor material
Pure insulating rubber
Solid silver
Porcelain

Question 25: The main characteristic that makes a material a "good conductor" is having:

Many free electrons that can move easily to carry current
A high melting point only
A shiny surface appearance only
Heavy physical weight

EXAM CARD BASIC

Questions25

Time limit38 min

Pass score75%

Code editionNEC 2023

DifficultyIntermediate

Last reviewedJun 2026

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Source: NEC 2026 (NFPA 70)