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Technician Course, Module 3: Electricity You Can Use
Covers NCVEC 2026-2030 Technician Pool, Subelement T5 (Electrical Principles). Four questions on your exam come from this material.
On the bench in Ray's shack sits a military surplus ammo can with a battery inside, a fuse block, a pair of Powerpole connectors, and a master switch. "Field power box," he says. "Before the weekend is over you are going to tell me what size fuse it needs. Not guess. Calculate."
To do that, you need four ideas and one law. That is this entire module.
3.1The Four Ideas
Current is the flow of electrons through a circuit. It is measured in amperes (amps, A). When Ray's radio transmits, electrons are flowing from the battery, through the radio, and back. More flow, more amps.
Voltage is the force that causes electrons to flow, measured in volts (V). Think of it as electrical pressure. A 12-volt battery pushes harder than a 1.5-volt flashlight cell. No voltage, no current.
Resistance is the opposition to that flow, measured in ohms. Everything resists at least a little, and resistance opposes every kind of current: DC, AC, and RF alike.
Power is the rate at which electrical energy is used, measured in watts (W). It is what heats the final transistors and what actually leaves the antenna.
Two supporting facts round out the vocabulary. Current that flows in one direction only is direct current (DC), which is what batteries deliver. Current that reverses, flowing between positive and negative directions, is alternating current (AC), which is what comes out of the wall. The number of complete cycles an alternating current makes per second is its frequency, measured in hertz (Hz). A radio signal is just alternating current cycling millions of times per second.
Why do electrons flow easily through wire but not through the wire's insulation? Metals are good conductors because they have many free electrons, loosely bound and ready to move. Insulators like glass hold their electrons tightly, so almost nothing flows.
Knowledge Check 3.1
Tap an answer. In your own words first, then check yourself.
1. What is electrical current, and what unit measures it?
2. What force causes electrons to flow in a circuit?
3. Why are metals good conductors?
T5A 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.
T5A01 Electrical current is measured in which of the following units?
Answer Amperes
Tip Current is measured in amperes, so think amps for how much charge is moving.
T5A02 Electrical power is measured in which of the following units?
Answer Watts
Tip Power is measured in watts. If you are talking how much work gets done, think watts.
T5A03 What is the term for the flow of electrons in an electric circuit?
Answer Current
Tip Current is the flow of electrons through the circuit, like water moving in a pipe.
T5A04 What term describes the number of times per second that an alternating current makes a complete cycle?
Answer Frequency
Tip Frequency counts how many full cycles happen each second.
T5A05 A difference in which of the following causes electron flow?
Answer Voltage
Tip Voltage is the push, the difference in pressure that makes electrons move.
T5A06 What is the unit of frequency?
Answer Hertz
Tip Frequency is measured in hertz, where one hertz is one cycle per second.
T5A07 Why are metals generally good conductors of electricity?
Answer They have many free electrons
Tip Metals conduct well because they are full of free electrons ready to move.
T5A08 Which of the following is a good electrical insulator?
Answer Glass
Tip Glass is a good insulator, which is why it holds charge back instead of passing it.
T5A09 Which of the following describes alternating current?
Answer Current that alternates between positive and negative directions
Tip Alternating current keeps swapping direction, flowing positive then negative over and over.
T5A10 Which term describes the rate at which electrical energy is used?
Answer Power
Tip Power is the rate that electrical energy gets used up.
T5A11 What type of current flow is opposed by resistance?
Answer All these choices are correct
Tip Resistance opposes current no matter its form, so AC, DC, and all of them count.
3.2Moving the Decimal Point
Radio numbers span from billionths to billions, so we handle them with metric prefixes. There are only four you need, plus one guest appearance:
- kilo (k) = one thousand. 1 kilovolt = 1000 volts. 1500 kHz = 1,500,000 Hz.
- mega (M) = one million. 3.525 MHz = 3525 kHz. 28400 kHz = 28.400 MHz.
- milli (m) = one one-thousandth. 1.5 amperes = 1500 milliamperes. 500 milliwatts = 0.5 watts.
- micro (µ) = one one-millionth. 1 microvolt = one one-millionth of a volt.
- pico (p) = one one-trillionth, seen with capacitors: 1,000,000 picofarads = 1 microfarad.
Ray's method: do not memorize conversions, memorize the ladder. Each step from milli to base to kilo to mega is a factor of 1000, which means the decimal point slides three places per step. Going up the ladder (milli to amps), slide it left. Going down (amps to milli), slide it right.
The second half of this section is the decibel (dB), the way radio people compare power levels. Decibels are logarithmic, which sounds scary and is not, because you only need three anchors:
- 3 dB = double the power. 5 watts to 10 watts is 3 dB.
- 10 dB = ten times the power. 20 watts to 200 watts is 10 dB.
- Negative works the same in reverse: 12 watts down to 3 watts is two halvings, or -6 dB.
Stack them for everything else. 100 times the power? That is 10 dB + 10 dB = 20 dB. Four times? 3 + 3 = 6 dB.
Knowledge Check 3.2
Tap an answer. In your own words first, then check yourself.
1. Your handheld draws 1.4 amperes on transmit. How many milliamperes is that?
2. You upgrade from a 5-watt handheld to a 50-watt mobile. What is the power increase in dB?
3. Which is the same as 28400 kHz?
T5B the easy way: all 13 questions, with the right answer
Every pool question in this group. Read the answer, let the tip make it stick.
T5B01 How many milliamperes is 1.5 amperes?
Answer 1500 milliamperes
Tip Milli means one thousandth, so multiply amps by 1000. 1.5 A is 1500 mA.
T5B02 Which is equal to 1,500,000 hertz?
Answer 1500 kHz
Tip Kilo is a thousand, so divide hertz by 1000. 1,500,000 Hz is 1500 kHz.
T5B03 Which is equal to one kilovolt?
Answer One thousand volts
Tip Kilo means a thousand, so one kilovolt is simply 1000 volts.
T5B04 Which is equal to one microvolt?
Answer One one-millionth of a volt
Tip Micro means one millionth, so a microvolt is one one-millionth of a volt.
T5B05 Which is equal to 500 milliwatts?
Answer 0.5 watts
Tip Milli is a thousandth, so divide by 1000. 500 mW is 0.5 watts.
T5B06 Which is equal to 3000 milliamperes?
Answer 3 amperes
Tip Milli means a thousandth, so divide by 1000. 3000 mA is 3 amperes.
T5B07 Which is equal to 3.525 MHz?
Answer 3525 kHz
Tip Mega is a million and kilo is a thousand, so move three places. 3.525 MHz is 3525 kHz.
T5B08 Which is equal to 1,000,000 picofarads?
Answer 1 microfarad
Tip A microfarad is a million picofarads, so 1,000,000 pF equals 1 uF.
T5B09 Which decibel value most closely represents a power increase from 5 watts to 10 watts?
Answer 3 dB
Tip Doubling the power is always 3 dB, so 5 watts up to 10 watts is 3 dB.
T5B10 Which decibel value most closely represents a power decrease from 12 watts to 3 watts?
Answer -6 dB
Tip Each halving is minus 3 dB, and 12 to 3 watts halves twice, so that is -6 dB.
T5B11 Which decibel value represents a power increase from 20 watts to 200 watts?
Answer 10 dB
Tip A ten times power jump is always 10 dB, so 20 watts to 200 watts is 10 dB.
T5B12 Which is equal to 28400 kHz?
Answer 28.400 MHz
Tip Kilo to mega moves three decimal places left, so 28400 kHz is 28.400 MHz.
T5B13 Which is equal to 2425 MHz?
Answer 2.425 GHz
Tip Mega to giga moves three places left, so 2425 MHz is 2.425 GHz.
3.3The One Law
Ray writes three letters on the whiteboard in a triangle: E on top, I and R on the bottom.
Ohm's Law ties voltage (E), current (I), and resistance (R) together. Cover the one you want, and the triangle shows you the math:
- E = I x R (voltage = current times resistance)
- I = E / R (current = voltage divided by resistance)
- R = E / I (resistance = voltage divided by current)
Then he fires drills at you until the triangle is reflex:
- 90 volts pushing 3 amps: R = 90 / 3 = 30 ohms.
- 12 volts across a circuit drawing 1.5 amps: R = 12 / 1.5 = 8 ohms.
- 120 volts across 80 ohms: I = 120 / 80 = 1.5 amps.
- 200 volts across 100 ohms: I = 200 / 100 = 2 amps.
- 0.5 amps through 2 ohms: E = 0.5 x 2 = 1 volt.
- 2 amps through 10 ohms: E = 2 x 10 = 20 volts.
Every exam version asks at least one of these, and they are free points for anyone who can divide.
Last concept: how components share a circuit. In a series circuit, components are in a single line, so the current is the same through all of them. In a parallel circuit, components sit side by side across the same two points, so the voltage is the same across all of them. Ray's shorthand: series shares current, parallel shares voltage.
Knowledge Check 3.3
Tap an answer. In your own words first, then check yourself.
1. A mobile radio draws 10 amps from a 12-volt system. What is the effective resistance of the load?
2. What current flows through a 24-ohm resistor connected across 240 volts?
3. In which circuit type is the voltage the same across every component?
T5D the easy way: all 14 questions, with the right answer
Every pool question in this group. Read the answer, let the tip make it stick.
T5D01 What formula is used to calculate current in a circuit?
Answer I = E / R
Tip Ohm's law for current is I = E / R, voltage divided by resistance.
T5D02 What formula is used to calculate voltage in a circuit?
Answer E = I x R
Tip Ohm's law for voltage is E = I x R, current times resistance.
T5D03 What formula is used to calculate resistance in a circuit?
Answer R = E / I
Tip Ohm's law for resistance is R = E / I, voltage divided by current.
T5D04 What is the resistance of a circuit in which a current of 3 amperes flows when connected to 90 volts?
Answer 30 ohms
Tip R = E / I, so 90 volts over 3 amps is 30 ohms.
T5D05 What is the resistance of a circuit for which the applied voltage is 12 volts and the current flow is 1.5 amperes?
Answer 8 ohms
Tip R = E / I, so 12 volts over 1.5 amps is 8 ohms.
T5D06 What is the resistance of a circuit that draws 4 amperes from a 12-volt source?
Answer 3 ohms
Tip R = E / I, so 12 volts over 4 amps is 3 ohms.
T5D07 What is the current in a circuit with an applied voltage of 120 volts and a resistance of 80 ohms?
Answer 1.5 amperes
Tip I = E / R, so 120 volts over 80 ohms is 1.5 amperes.
T5D08 What is the current through a 100-ohm resistor connected across 200 volts?
Answer 2 amperes
Tip I = E / R, so 200 volts over 100 ohms is 2 amperes.
T5D09 What is the current through a 24-ohm resistor connected across 240 volts?
Answer 10 amperes
Tip I = E / R, so 240 volts over 24 ohms is 10 amperes.
T5D10 What is the voltage across a 2-ohm resistor if a current of 0.5 amperes flows through it?
Answer 1 volt
Tip E = I x R, so 0.5 amps times 2 ohms is 1 volt.
T5D11 What is the voltage across a 10-ohm resistor if a current of 1 ampere flows through it?
Answer 10 volts
Tip E = I x R, so 1 amp times 10 ohms is 10 volts.
T5D12 What is the voltage across a 10-ohm resistor if a current of 2 amperes flows through it?
Answer 20 volts
Tip E = I x R, so 2 amps times 10 ohms is 20 volts.
T5D13 In which type of circuit is the current always the same through all components?
Answer Series
Tip In a series circuit the same current flows through every part, one single path.
T5D14 In which type of circuit is the voltage always the same across all components?
Answer Parallel
Tip In a parallel circuit every branch sees the same voltage across it.
3.4Power Math and Two Energy Tanks
Back to the ammo can. "The radio manual says 22 amps max draw at 13.8 volts," Ray says. "How much power is that?"
The power formula: P = I x E (power = current times voltage). So 22 x 13.8 is right around 300 watts of DC input. The pool versions you should be able to do cold:
- 13.8 volts at 10 amps: 138 watts.
- 12 volts at 2.5 amps: 30 watts.
- And in reverse: how much current delivers 120 watts at 12 volts? I = P / E = 120 / 12 = 10 amps.
That reverse version is the one you will use constantly, because it converts a radio's power rating into the current its wiring and fuses must carry.
Two more components store energy instead of using it, and the exam wants their vocabulary:
- Capacitance is the ability to store energy in an electric field, measured in farads. Capacitors are the sprinters: charge fast, dump fast.
- Inductance is the ability to store energy in a magnetic field, measured in henrys. Inductors are coils of wire, and they resist changes in current.
And one word that will follow you all the way to Extra class: impedance, the opposition to AC current flow, measured in ohms. Your radio expects to see about 50 ohms of it looking into the feed line. For now, just own the definition and the unit.
Housekeeping the exam checks: the correct abbreviations are kHz (lowercase k, capital H, lowercase z) and MHz (capital M, capital H, lowercase z). RF is alternating current at radio frequencies, and its unit of frequency is still the hertz.
Knowledge Check 3.4
Tap an answer. In your own words first, then check yourself.
1. Your radio manual lists 20 amps of transmit current draw on a 13.8-volt supply. Approximately how much power is that?
2. Which component stores energy in a magnetic field, and what is its unit?
3. What is impedance?
T5C 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.
T5C01 What describes the ability to store energy in an electric field?
Answer Capacitance
Tip Capacitance is the ability to store energy in an electric field, the job of a capacitor.
T5C02 What is the unit of capacitance?
Answer Farad
Tip Capacitance is measured in farads.
T5C03 What describes the ability to store energy in a magnetic field?
Answer Inductance
Tip Inductance stores energy in a magnetic field, the job of a coil.
T5C04 What is the unit of inductance?
Answer Henry
Tip Inductance is measured in henrys.
T5C05 What is the unit of impedance?
Answer Ohm
Tip Impedance is measured in ohms, the same unit as plain resistance.
T5C06 What is the abbreviation for kilohertz?
Answer kHz
Tip Kilohertz shortens to kHz, with a lowercase k and a capital H.
T5C07 What is the abbreviation for megahertz?
Answer MHz
Tip Megahertz shortens to MHz, with a capital M for mega.
T5C08 What formula is used to calculate electrical power (P) in a DC circuit?
Answer P = I x E
Tip DC power is P = I x E, current times voltage.
T5C09 How much power is delivered by a voltage of 13.8 volts DC and a current of 10 amperes?
Answer 138 watts
Tip P = I x E, so 10 amps times 13.8 volts gives 138 watts.
T5C10 How much power is delivered by a voltage of 12 volts DC and a current of 2.5 amperes?
Answer 30 watts
Tip P = I x E, so 2.5 amps times 12 volts gives 30 watts.
T5C11 How much current is required to deliver 120 watts at a voltage of 12 volts DC?
Answer 10 amperes
Tip Rearrange P = I x E to I = P / E, so 120 watts over 12 volts is 10 amperes.
T5C12 What is impedance?
Answer The opposition to AC current flow
Tip Impedance is the opposition to AC current flow, resistance and reactance combined.
Review: every Exam Anchor from this module
T5A Current: flow of electrons, measured in amperes. Voltage: the force that causes electron flow, measured in volts. Power: the rate at which electrical energy is used, measured in watts. Frequency: cycles per second of an alternating current, measured in hertz. DC flows one direction, AC alternates between positive and negative directions. Metals conduct because of many free electrons; glass is a good insulator. Resistance opposes all current: DC, AC, and RF.
T5B 1.5 A = 1500 mA. 1,500,000 Hz = 1500 kHz. 1 kV = 1000 V. 1 µV = one millionth of a volt. 500 mW = 0.5 W. 3000 mA = 3 A. 3.525 MHz = 3525 kHz. 28400 kHz = 28.400 MHz. 2425 MHz = 2.425 GHz. 1,000,000 pF = 1 µF. Decibels: 3 dB doubles power (5 W to 10 W), 10 dB is ten times (20 W to 200 W), 12 W to 3 W is -6 dB.
T5D E = I x R, I = E / R, R = E / I. Worked values above match the pool problems. Series circuit: same current through all components. Parallel circuit: same voltage across all components.
T5C P = I x E. 13.8 V at 10 A = 138 W. 12 V at 2.5 A = 30 W. 120 W at 12 V requires 10 A. Capacitance: energy stored in an electric field, unit farad. Inductance: energy stored in a magnetic field, unit henry. Impedance: opposition to AC current flow, unit ohm. Abbreviations: kHz and MHz.
Before you move on
You can now speak the language (volts, amps, ohms, watts), slide decimal points with the metric prefixes, use dB anchors to compare power, work the Ohm's Law triangle, and calculate power and current for real equipment. Ray's fuse question is now answerable: a radio drawing 22 amps needs wiring and a fuse rated comfortably above that, and you calculated it rather than guessed.
Module 4 opens the parts bin: resistors, capacitors, inductors, diodes, transistors, and the schematic symbols that let you read a circuit like a map.
© 2026 Anthony Pelfanio, K4DIA. All rights reserved.