T5: Electrical Principles – Ham Radio Technician License Study Guide

Amateur radio is built on electricity — every transmission, every reception, every component in your station is governed by the same electrical principles that have been understood since the 19th century. T5 grounds you in those principles: the definitions, units, formulas, and relationships that make radio equipment understandable and predictable.

Four exam questions are drawn from this subelement, one from each group. T5A covers the core vocabulary: current, voltage, resistance, power, frequency, conductors, insulators, and alternating vs. direct current. T5B covers the math of electronics: unit prefixes and conversions (milli, kilo, micro, mega, giga) and decibel calculations for power changes. T5C covers the definitions and units for capacitance, inductance, and impedance, along with the RF terminology and the power formula for DC circuits. T5D covers Ohm's Law — the three forms of the formula and applying it to solve for current, voltage, or resistance — plus the key properties of series and parallel circuits.

T5A: Current and Voltage

T5A establishes the foundational vocabulary of electricity. Current is the flow of electrons in a circuit, measured in amperes. Voltage is the electrical force that drives electron flow, measured in volts. Resistance opposes current flow, measured in ohms. Power is the rate at which electrical energy is used, measured in watts. Frequency — how many times per second an alternating current completes a full cycle — is measured in hertz. Metals are good conductors because they have many free electrons; glass is a good insulator because it has very few. Alternating current reverses direction — it flows in positive and negative directions alternately, unlike direct current which flows continuously in one direction. Resistance opposes all types of current flow: DC, AC, and RF.

T5B: Math for Electronics

T5B covers the unit prefix system used throughout electronics and the decibel scale for expressing power ratios. The metric prefix system scales units by factors of 1000: milli = one-thousandth, kilo = one thousand, mega = one million, giga = one billion, micro = one-millionth, pico = one-trillionth. Converting between units requires moving the decimal point in the appropriate direction. For decibels: doubling power equals +3 dB, halving power equals -3 dB, a factor of 10 increase equals +10 dB, a factor of 4 decrease (one-quarter power) equals -6 dB.

T5C: Capacitance, Inductance, and Power

T5C introduces three additional electrical quantities and their units, reinforces RF terminology, and covers the DC power formula. Capacitance is the ability to store energy in an electric field; its unit is the farad. Inductance is the ability to store energy in a magnetic field; its unit is the henry. Impedance is the total opposition to AC current flow (combining resistance and reactance); its unit is the ohm. RF stands for radio frequency signals of all types. The correct abbreviation for megahertz is MHz; for kilohertz, kHz. The DC power formula is P = I × E (power equals current times voltage). Impedance should not be confused with resistance — impedance applies to AC circuits and includes reactive effects from capacitors and inductors.

T5D: Ohm's Law and Circuits

T5D covers Ohm's Law and circuit topology. Ohm's Law relates current (I), voltage (E), and resistance (R) in three equivalent forms: I = E / R (to find current), E = I × R (to find voltage), R = E / I (to find resistance). In a series circuit, the same current flows through every component. In a parallel circuit, the same voltage appears across every component. These circuit properties are fundamental to understanding how components combine in real stations.

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