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Technician Course, Module 4: The Parts Bin
Covers NCVEC 2026-2030 Technician Pool, Subelement T6 (Electrical and Electronic Components). Four questions on your exam come from this material.
Ray dumps a coffee can of parts onto the bench: striped little cylinders, tiny tan discs, coils of wire, black plastic bugs with three legs. "Every radio ever built is made of maybe a dozen kinds of parts," he says. "Learn what each one does and no circuit will ever be a mystery box again."
4.1The Passive Parts
Resistors oppose the flow of current. That is the whole job. Need less current through an LED? Put a resistor in front of it. A resistor built to be adjustable is a potentiometer, and you have used one your whole life: the volume control on a radio is a potentiometer varying resistance as you turn it.
Capacitors store energy in an electric field. Physically, a capacitor is two conductive surfaces separated by an insulator. Charge builds on the plates, ready to dump back out quickly.
Inductors store energy in a magnetic field, and they are typically constructed as a coil of wire. Current through the coil builds the field; interrupt the current and the field collapses, pushing back.
If those definitions sound familiar, they should. Farads and henrys from Module 3 were the units. These are the parts.
Switches route current. The naming tells you everything: poles are how many separate circuits the switch controls, throws are how many positions each pole can connect to. A single-pole single-throw (SPST) switch opens or closes one circuit. A single-pole double-throw (SPDT) switch connects one circuit to either of two other circuits. Your master disconnect on a battery box is an SPST doing its one honest job.
Batteries store chemical energy, and the exam sorts them into two piles. Rechargeable: nickel-metal hydride, lithium-ion, and lead-acid, all of them. Not rechargeable: carbon-zinc, the cheap disposable cells. Try to recharge those and you get leakage or worse.
Knowledge Check 4.1
Tap an answer. In your own words first, then check yourself.
1. The volume knob on a radio is most likely which component?
2. Which component is typically built as a coil of wire and stores energy in a magnetic field?
3. Which battery chemistry should never be recharged?
T6A the easy way: all 11 questions, with the right answer
Every pool question in this group. Read the answer, let the tip make it stick.
T6A01 What electrical component opposes the flow of current in a DC circuit?
Answer Resistor
Tip A resistor's whole job is to resist, so it opposes current flow in a DC circuit.
T6A02 What type of component is often used as an adjustable volume control?
Answer Potentiometer
Tip A potentiometer is a knob you turn to adjust resistance, which is why it makes a handy volume control.
T6A03 What electrical parameter is controlled by a potentiometer?
Answer Resistance
Tip Pot is short for potentiometer, and what it adjusts is resistance.
T6A04 What electrical component stores energy in an electric field?
Answer Capacitor
Tip A capacitor holds its charge as an electric field between two plates.
T6A05 What type of electrical component consists of conductive surfaces separated by an insulator?
Answer Capacitor
Tip Two conductive plates with an insulator between them is the recipe for a capacitor.
T6A06 What type of electrical component stores energy in a magnetic field?
Answer Inductor
Tip An inductor stores energy in a magnetic field, the magnetic cousin of the capacitor.
T6A07 What electrical component is typically constructed as a coil of wire?
Answer Inductor
Tip Wind wire into a coil and you have made an inductor.
T6A08 What is the function of an SPDT switch?
Answer A single circuit is switched between one of two other circuits
Tip SPDT means single pole double throw, so one input flips between two possible outputs.
T6A09 What type of switch is represented by component 3 in figure T-2?
Answer Single-pole single-throw
Tip SPST is the simplest switch, one circuit that is just on or off.
T6A10 Which of the following battery chemistries is rechargeable?
Answer All these choices are correct
Tip Think rechargeable across the board here, so all the listed chemistries qualify.
T6A11 Which of the following battery chemistries is not rechargeable?
Answer Carbon-zinc
Tip A carbon-zinc cell is a throwaway, use it once then toss it because it will not recharge.
4.2The Semiconductors
Now the parts that made modern radio possible.
A diode is a one-way valve: it allows current to flow in only one direction. Its two electrodes are the anode and the cathode, and on the physical package the cathode end is marked with a stripe. Push current the forward direction and the diode conducts, but it always keeps a small toll, called the forward voltage drop, and that drop is lower in some diode types than in others. One famous diode turns that forward current directly into light: the LED emits light when forward current flows through it.
A transistor is the part that changed the world. It can consist of three regions of semiconductor material, and it does two jobs:
- It can act as an electronic switch, turning current on and off with no moving parts.
- It can amplify, using a small signal to control a larger one. A component that can provide power gain is a transistor, and gain means the output signal (voltage, current, or power) relative to the input signal. All of those definitions are correct at once.
Two families of transistor, two sets of leg names, and the exam checks both:
- Bipolar junction transistor (BJT): emitter, base, collector.
- Field-effect transistor (FET): gate, drain, source. FET literally stands for Field Effect Transistor.
Ray's mnemonic: the FET names sound like plumbing (gate, drain, source) because a FET works like a valve, with the gate voltage controlling flow from source to drain.
Knowledge Check 4.2
Tap an answer. In your own words first, then check yourself.
1. Which component allows current to flow in only one direction?
2. What are the three electrodes of a bipolar junction transistor?
3. What makes an LED light up?
T6B the easy way: all 12 questions, with the right answer
Every pool question in this group. Read the answer, let the tip make it stick.
T6B01 Which is true about forward voltage drop in a diode?
Answer It is lower in some diode types than in others
Tip Different diode types drop different forward voltages, so that drop is not one fixed number.
T6B02 What electronic component allows current to flow in only one direction?
Answer Diode
Tip A diode is a one-way valve for current, letting it pass in only one direction.
T6B03 Which of these components can be used as an electronic switch?
Answer Transistor
Tip A transistor can switch a circuit on and off electronically, no moving parts needed.
T6B04 Which of the following components can consist of three regions of semiconductor material?
Answer Transistor
Tip A transistor is built from three regions of semiconductor material stacked together.
T6B05 What type of transistor has a gate, drain, and source?
Answer Field-effect
Tip Gate, drain, and source are the three terminals of a field-effect transistor.
T6B06 How is the cathode lead of a semiconductor diode often marked on the package?
Answer With a stripe
Tip Look for the stripe on a diode, it marks the cathode end.
T6B07 What causes a light-emitting diode (LED) to emit light?
Answer Forward current
Tip Push forward current through an LED and it lights up.
T6B08 What does the abbreviation FET stand for?
Answer Field Effect Transistor
Tip FET simply spells out Field Effect Transistor.
T6B09 What are the names for the electrodes of a diode?
Answer Anode and cathode
Tip A diode has two electrodes, the anode and the cathode.
T6B10 Which of the following can provide power gain?
Answer Transistor
Tip A transistor can give power gain, turning a small signal into a bigger one.
T6B11 What does the term gain mean in amplifiers?
Answer All these choices are correct
Tip Gain covers all those meanings, so the all choices answer is the safe pick.
T6B12 What are the names of the electrodes of a bipolar junction transistor?
Answer Emitter, base, collector
Tip A bipolar junction transistor has three leads, the emitter, base, and collector.
4.3Reading the Map
Ray unfolds a sheet of paper covered in lines and symbols. "This is a schematic. It is not a photograph of a circuit. It is a map of one."
A schematic is an electrical diagram that uses standard symbols for components. Here is the key idea the exam tests: what a schematic accurately represents is the component connections. It does not show wire lengths and it does not show what parts physically look like. Two schematics of the same circuit can be drawn completely differently and both be correct, as long as the connections match.
The standard symbols you must recognize on sight:
- Resistor: a zigzag line.
- Capacitor: two parallel lines with a gap.
- Inductor: a series of loops or humps.
- Diode: a triangle pointing into a bar (the bar end is the cathode, matching the stripe).
- LED: the diode symbol with two small arrows leaving it, light going out.
- Transistor: a circle with three leads, the emitter carrying an arrow.
- Battery: alternating long and short parallel lines.
- Lamp: a circle with a loop or cross inside.
- Switch: a line pivoting between contacts. Count poles and throws right on the drawing.
- Variable anything: an arrow drawn through the symbol. Arrow through a resistor is a potentiometer, arrow through an inductor is a variable inductor.
- Transformer: two inductor symbols facing each other, often with parallel lines between them.
- Antenna: the branching upward symbol at the end of the RF chain.
- Ground: descending horizontal lines, wide to narrow.
Website note: the exam includes three figures (T-1, T-2, T-3) that these questions point at. This page will include practice diagrams with each symbol labeled and an unlabeled version for self-testing.
The exam questions on figures are pure symbol recognition: point at a zigzag, answer resistor. Learn the symbols above and the figure questions are free points.
Quiz yourself: identify the basic symbols
Quiz yourself: identify the semiconductors
Quiz yourself: identify the variable components
Knowledge Check 4.3
Tap an answer. In your own words first, then check yourself.
1. What does a schematic accurately represent about a circuit?
2. A zigzag line on a schematic represents which component?
3. An arrow drawn through a component symbol generally means the component is:
T6C the easy way: all 12 questions, with the right answer
Every pool question in this group. Read the answer, let the tip make it stick.
T6C01 What is an electrical diagram using standard component symbols called?
Answer Schematic
Tip A schematic is the map of a circuit drawn with standard component symbols.
T6C02 What is component 1 in figure T-1?
Answer Resistor
Tip Component 1 is a resistor, shown as the little zigzag line.
T6C03 What is component 2 in figure T-1?
Answer Transistor
Tip Component 2 is a transistor, the three-lead amplifying device.
T6C04 What is component 3 in figure T-1?
Answer Lamp
Tip Component 3 is a lamp, drawn as an X or loop inside a circle.
T6C05 What is component 4 in figure T-1?
Answer Battery
Tip Component 4 is a battery, the long and short line symbol.
T6C06 What is component 6 in figure T-2?
Answer Capacitor
Tip Component 6 is a capacitor, shown as two parallel plates.
T6C07 What is component 8 in figure T-2?
Answer Light emitting diode
Tip Component 8 is a light emitting diode, a diode symbol with little arrows beaming out.
T6C08 What is component 9 in figure T-2?
Answer Variable resistor
Tip Component 9 is a variable resistor, a resistor with an arrow through it for adjusting.
T6C09 What is component 4 in figure T-2?
Answer Transformer
Tip Component 4 is a transformer, two coils drawn side by side sharing a core.
T6C10 What is component 3 in figure T-3?
Answer Variable inductor
Tip Component 3 is a variable inductor, a coil with an arrow showing it can be tuned.
T6C11 What is component 4 in figure T-3?
Answer Antenna
Tip Component 4 is an antenna, drawn as the little upward fork or triangle.
T6C12 Which of the following is accurately represented in electrical schematics?
Answer Component connections
Tip A schematic shows how parts connect, not their size or physical layout.
4.4Parts That Do a Job
The last group is functional parts, each defined by what it accomplishes:
- A rectifier changes alternating current into varying direct current. It is the diode's day job, and it is the heart of every power supply.
- A transformer changes 120 V AC power to a lower AC voltage. Two coils share a magnetic field; the turns ratio sets the voltage ratio. Rectifier plus transformer plus filtering is how wall power becomes radio power.
- A regulator is the circuit that controls the amount of voltage from a power supply, holding it steady as loads change.
- A relay is an electrically controlled switch: a small current energizes a coil, the coil pulls contacts closed, and a big current flows somewhere else. Your finger on the PTT ultimately throws relays.
- A meter displays an electrical quantity as a numeric value.
- An LED is the standard visual indicator on nearly every panel.
- An integrated circuit (IC) combines several semiconductors and other components into one package. An entire receiver can live in a chip the size of a fingernail.
- Shielded wire is used to prevent coupling of unwanted signals to or from the wire. The braid around the center conductor is a fence for signals.
- And the one that ties Module 3 and Module 4 together: combine an inductor and a capacitor, in series or in parallel, and you get a resonant circuit, also called a tuned circuit. The two energy tanks trade energy back and forth at one favorite frequency. Resonant circuits are how radios select one signal out of the entire spectrum, and you will meet them again in every license class you ever earn.
Knowledge Check 4.4
Tap an answer. In your own words first, then check yourself.
1. Which device changes alternating current into varying direct current?
2. What is a relay?
3. What two components form a resonant circuit?
T6D the easy way: all 11 questions, with the right answer
Every pool question in this group. Read the answer, let the tip make it stick.
T6D01 Which of the following devices or circuits changes an alternating current into a varying direct current signal?
Answer Rectifier
Tip A rectifier turns AC into pulsing DC, flipping the current so it flows one way.
T6D02 What is a relay?
Answer An electrically-controlled switch
Tip A relay is just a switch you flip with electricity instead of your finger.
T6D03 Which of the following is a reason to use shielded wire?
Answer To prevent coupling of unwanted signals to or from the wire
Tip Shielded wire keeps stray signals out and your signal in by surrounding the conductor.
T6D04 Which of the following displays an electrical quantity as a numeric value?
Answer Meter
Tip A meter reads out an electrical quantity as a number you can see.
T6D05 What type of circuit controls the amount of voltage from a power supply?
Answer Regulator
Tip A regulator holds the output voltage steady by controlling how much gets through.
T6D06 What component changes 120 V AC power to a lower AC voltage for other uses?
Answer Transformer
Tip A transformer steps 120 V AC down to a lower AC voltage for other uses.
T6D07 Which of the following is commonly used as a visual indicator?
Answer LED
Tip An LED makes a bright little visual indicator that sips very little power.
T6D08 Which of the following is combined with an inductor to make a resonant circuit?
Answer Capacitor
Tip Pair a capacitor with an inductor and you get a resonant circuit.
T6D09 What is the name of a device that combines several semiconductors and other components into one package?
Answer Integrated circuit
Tip An integrated circuit packs many semiconductors and parts into one chip.
T6D10 What is the function of component 2 in figure T-1?
Answer Control the flow of current
Tip That transistor's job in the circuit is to control the flow of current.
T6D11 Which of the following is a resonant or tuned circuit?
Answer An inductor and a capacitor in series or parallel
Tip A resonant or tuned circuit is just an inductor and capacitor together, in series or parallel.
Review: every Exam Anchor from this module
T6A Resistor: opposes current. Potentiometer: adjustable resistance, used as a volume control. Capacitor: conductive surfaces separated by an insulator, stores energy in an electric field. Inductor: coil of wire, stores energy in a magnetic field. SPDT switch: one circuit switched between one of two other circuits. Rechargeable chemistries: NiMH, lithium-ion, lead-acid. Not rechargeable: carbon-zinc.
T6B Diode: current flows one direction only; electrodes are anode and cathode; cathode marked with a stripe; forward voltage drop differs between diode types; an LED emits light from forward current. Transistor: three semiconductor regions, works as an electronic switch, provides power gain. Gain: output relative to input (voltage, current, or power). BJT leads: emitter, base, collector. FET leads: gate, drain, source. FET = Field Effect Transistor.
T6C A schematic is an electrical diagram using standard component symbols. Schematics accurately represent component connections, not wire lengths or physical appearance. Be able to identify on sight: resistor, transistor, lamp, battery, capacitor, LED, variable resistor (potentiometer), transformer, variable inductor, antenna.
T6D Rectifier: changes AC into varying DC. Relay: electrically controlled switch. Regulator: controls power supply voltage. Transformer: converts 120 V AC to lower AC voltage. Meter: displays a value numerically. LED: common visual indicator. Integrated circuit: multiple semiconductors and components in one package. Shielded wire: prevents unwanted signal coupling. Resonant (tuned) circuit: an inductor and capacitor in series or parallel. A resistor's function in a circuit: control the flow of current.
Before you move on
The coffee can of parts is now a vocabulary: passives that resist and store, semiconductors that steer and amplify, symbols that map them, and functional parts defined by their jobs. The resonant circuit, an inductor and capacitor trading energy, is the single most important idea to carry forward, because it is how every radio chooses a frequency.
Module 5 assembles these parts into an actual radio and teaches you what to do when it misbehaves.
© 2026 Anthony Pelfanio, K4DIA. All rights reserved.