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BASIC NEC 2023

Diodes, Rectifiers & Basic Solid-State Devices Practice Test

Free online diodes, rectifiers, and solid-state devices practice test. 25 basic electrical questions on diode bias, rectification, Zener diodes, LEDs, transistors, and SCRs. Good for electrician exam prep.

TOPICS COVERED

Diode Basics Diode Terminals Forward Bias Reverse Bias Diode Forward Voltage Diode Rectification Use

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A diode is the simplest solid-state device: a one-way valve for current, conducting when forward biased and blocking when reverse biased. Their most common electrical job is rectification — converting AC to DC, either with a single diode (half-wave) or a four-diode bridge (full-wave). Special-purpose diodes expand on this: a Zener diode regulates voltage by working in controlled reverse breakdown, and an LED emits light when forward biased. A transistor adds a third terminal for switching or amplifying signals, and an SCR (thyristor) is a diode-like device that needs a gate signal before it will conduct — the basis of motor soft starters and light dimmers.

25

Questions

38 min

Time

75%

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Diodes, Rectifiers & Basic Solid-State Devices Practice Test — Question List

Question 1: A diode is a semiconductor device that:

Allows current to flow in only one direction
Allows current to flow equally in both directions
Blocks all current in every direction, always
Stores energy in a magnetic field

Question 2: The two terminals of a diode are called the:

Anode and cathode
Base and collector
Line and neutral
Hot and ground

Question 3: A diode is "forward biased" when:

Voltage is applied in the direction that allows the diode to conduct current
Voltage is applied in the direction that blocks the diode from conducting
No voltage is applied to the diode at all
The diode is physically disconnected from the circuit

Question 4: A diode is "reverse biased" when:

Voltage is applied in the direction that blocks current flow through the diode
Voltage is applied in the direction that allows maximum current flow
The diode is heated to a very high temperature
The diode is being used as an LED

Question 5: A typical silicon diode has a forward voltage drop of approximately:

0.7 volts
12 volts
120 volts
0 volts

Question 6: One of the most common uses of a diode in electrical equipment is:

Rectification — converting AC current into DC current
Increasing the system frequency above 60 Hz
Storing large amounts of magnetic energy
Converting single-phase power into three-phase power

Question 7: A half-wave rectifier uses a single diode to:

Pass only one half of the AC waveform, blocking the other half
Pass the complete, unmodified AC waveform
Block the AC waveform completely at all times
Double the frequency of the AC waveform

Question 8: A full-wave bridge rectifier improves on a half-wave rectifier by:

Using both halves of the AC waveform to produce a smoother, more usable DC output
Using none of the AC waveform at all
Only working with DC input, never AC
Requiring no diodes whatsoever

Question 9: A standard full-wave bridge rectifier circuit uses how many diodes?

Four
One
Two
Eight

Question 10: A diode's Peak Inverse Voltage (PIV) rating indicates:

The maximum reverse voltage the diode can withstand before it breaks down
The exact forward current the diode will always draw
The physical size of the diode package
The diode's resistance when fully forward biased

Question 11: Unlike a standard diode, a Zener diode is specifically designed to:

Operate safely in reverse breakdown, making it useful for voltage regulation
Only conduct current when completely disconnected
Convert DC current into three-phase AC current
Store large amounts of magnetic energy

Question 12: An LED (light-emitting diode) is a diode that:

Emits light when forward biased and conducting current
Emits light only when reverse biased
Never emits any light under any condition
Converts light directly into AC power

Question 13: Like other diodes, an LED must be installed with correct polarity because:

It will only conduct current (and light up) when forward biased
It works exactly the same no matter which way it is connected
It requires no electrical connection to function
It only operates correctly on three-phase power

Question 14: In a DC power supply, a filter capacitor placed after a rectifier is used to:

Smooth out the pulsating rectified output into a steadier DC voltage
Convert the DC output back into AC
Increase the output frequency
Block all current from reaching the load

Question 15: A transistor is a semiconductor device that is commonly used for:

Switching or amplifying electronic signals
Storing large amounts of mechanical energy
Converting light directly into sound
Measuring magnetic field strength only

Question 16: A standard bipolar junction transistor (BJT) has three terminals named:

Base, collector, and emitter
Anode, cathode, and gate
Line, neutral, and ground
Hot, common, and travel

Question 17: When used as a simple switch, a transistor can be turned fully ON or fully OFF by:

Applying or removing a small control signal at its base terminal
Physically removing the transistor from the circuit board
Changing the color of the transistor casing
Increasing the ambient room temperature

Question 18: NPN and PNP are two basic types of bipolar transistors that differ mainly in:

The arrangement and polarity of their semiconductor layers, which affects how they are biased
NPN transistors cannot conduct any current at all
PNP transistors only function in DC circuits above 1000 V
There is no real difference between the two types

Question 19: A thyristor (SCR) is a semiconductor device commonly used in applications like motor soft starters because it can:

Control how much of an AC waveform is allowed through, based on a triggering (gate) signal
Permanently block all current in both directions
Only function correctly on pure DC systems
Emit visible light like an LED

Question 20: Unlike a standard diode, a Silicon Controlled Rectifier (SCR) requires:

A gate signal to trigger it into conduction, even when it is otherwise forward biased
No control signal of any kind, ever
A constant reverse voltage to stay conducting
Physical rotation to begin conducting

Question 21: A triac differs from an SCR in that a triac:

Can conduct current in both directions, making it useful for controlling full AC waveforms, such as in light dimmers
Can only conduct DC current, never AC
Cannot be triggered by any gate signal
Is identical to an SCR in every respect

Question 22: When troubleshooting a suspected failed diode with an ohmmeter on a de-energized circuit, a diode that reads very low resistance in BOTH directions is most likely:

Shorted (failed)
Working perfectly normally
Open (failed) in both directions
Impossible to determine with an ohmmeter

Question 23: A photodiode (or photocell) is a semiconductor device that:

Changes its electrical behavior in response to light striking it
Changes its electrical behavior in response to sound only
Never responds to any external condition
Only functions correctly in complete darkness

Question 24: Diodes are commonly found in which of the following pieces of electrical equipment?

Battery chargers and DC power supplies
Plain incandescent light bulbs
Uninsulated bare copper grounding wire
Wooden ladders

Question 25: As with any electronic component in a de-energized circuit, before handling diodes and rectifier assemblies that were recently in service, an electrician should be aware that they may still be:

Hot to the touch from recent operation, even though electrically de-energized
Completely and instantly safe to touch the moment power is off
Radioactive and hazardous to be near at any time
Guaranteed to explode on contact

EXAM CARD BASIC

Questions25

Time limit38 min

Pass score75%

Code editionNEC 2023

DifficultyIntermediate

Last reviewedJun 2026

Timer starts immediately. Progress is auto-saved.

Source: NEC 2026 (NFPA 70)