Electronics Information Study Guide for the ASVAB

General Information

The Electronics Information section of the ASVAB test covers various items, ranging from questions regarding wires and gauges to questions concerning basic electrical functions. To prepare for this portion of the test, study basic electronic information such as how wires function, the function of different electrical currents and conductors, and Ohm’s law. Learn more information about each of these areas below.

A significant portion of the electronics test contains questions on vocabulary, assessing students’ ability to recognize simple electrical vocabulary words. When studying ASVAB concepts, focus on the basic definitions of electrical words and terminology, including the aforementioned concepts and appliance-specific words, such as voltage and frequency. When studying for the vocabulary portion, focus on the bare bones of concept definitions to recognize what a certain word or phrase means.

If you take the CAT version of the ASVAB, you’ll have 10 minutes to answer 15 Electronics Information questions. The paper-and-pencil test version gives you 20 questions to answer in 15 minutes.

Electron Flow Theory

Electron flow theory describes the behavior of electrons when moving through a conductor. Negatively charged electrons in a circuit flow from the negative terminal (or anode) to the positive terminal (or cathode). Electrons flow in this manner in response to the attractive and repulsive forces between charged particles.

Atoms, Protons, Neutrons, Electrons, and Valence Shell

All matter is made of smaller particles called atoms. Atoms display different properties depending on the composition of the atom. They are composed of smaller particles called protons, electrons, and neutrons. A single proton is an element known as hydrogen. The addition of another proton results in a new element known as helium. If, instead, there is a different number of neutrons inside of the nucleus (the protons and neutrons in an atom), then it is known as an isotope.

The three particles inside of the atom differ in interesting ways: protons and electrons are oppositely charged, and neutrons do not possess charge; protons and neutrons are similarly sized and constitute a vast majority of the atom’s density.

Electrons are much smaller than protons and neutrons and exist around the nucleus inside of energy orbitals. These energy orbitals surround the nucleus depending upon the number of electrons and their distance from the atomic nucleus. These electrons farthest from the nucleus are the most reactive.

Conductor, Semiconductor, and Insulator

Conductivity measures the ease with which electrons can flow through a material. Metals are good conductors because electrons flow easily through them without much resistance. Copper is an excellent example of a conductor. Copper wire conducts current with little resistance.

Materials exhibiting very low conductivity are called insulators. Insulators possess high resistivity. Rubber is a good example of an insulator. Many tools used in electrical work have rubber-coated handles.

Semiconductors have conductivities that are between those of conductors and insulators. Unlike conductors, which experience increased resistance when heated, semiconductors increase in conductivity when heated. Graphite, which is used to make many resistors, is a good example of a semiconductor.

Current

Current is the rate at which charges flow through a portion of a conductor in an electric circuit. It is measured in coulombs per second, or amperes. Current, voltage, and resistance are related to each other through Ohm’s law:

\[I = \frac{V}{R}\]

where I is current, V is voltage, and R is resistance.

Voltage

Voltage is the electric potential difference between two charged points in an electric field. Because it is a difference in potential, voltage is only meaningful when considering one point in relation to another. It is measured in volts.

Voltage is also referred to as the electromotive force, as it is the force responsible for driving the current through a circuit. It can be likened to a difference in pressure because there is a higher concentration of charge at one point than another. This difference in charge concentration results in a voltage.

Resistance

Resistance is an inherent property of materials that hinders the passage of current through a conductor. Resistance and conductance are inversely related; a very conductive material has little resistance, and a very resistive material has little conductance. Resistance is measured in ohms.

Materials vary in resistance because of the ease (or difficulty) with which electrons in the material’s atom can be displaced. Resistance is also linked to the cross-sectional area and length of the material used; the larger the area, the lesser the resistance, and the longer the conductor, the greater the resistance.

Quantitatively, resistance can be represented as:

\[R = ⍴ \cdot \frac{L}{A}\]

where \(⍴\) represents the resistivity of the conducting material, L is the length, and A is the cross-sectional area.

Circuits

A voltage source, such as a battery, with conducting materials, such as insulated wires, attached to and connecting both terminals forms a circuit. This circuit would, of course, do nothing but heat the conducting wires.

Connecting a load, such as a resistor or a light bulb, to the wires enables the current to perform work. These loads can be connected to the circuit in series, in parallel, or in series-parallel.

Closed and Open Circuits

A closed circuit is one in which all of the components of the circuit are connected via conducting wires to each other and a voltage source. If any of these connections are broken, the circuit is said to be open and will not function properly. A closed circuit can work; an open circuit cannot.

Load

A load is any component that drains power from a circuit. Light bulbs, refrigerators, and computers all act as loads when part of a closed circuit. Loads only dissipate power from a circuit; they do not generate power.

Series Circuit

In a series circuit, all of the components are connected one after the other. The current that runs through a series circuit passes through each component in series. There is only a single path for the current to take through the circuit.

The total voltage and total resistance in a series circuit is the sum of the voltage drops across each component and the sum of the resistances in the circuit, respectively. The sum of each resistance in the circuit is called the equivalent resistance, or \(R_{eq}\), and because there is only one current in the circuit, it is the \(R_{eq}\) that is used in Ohm’s law calculations for series circuits.

Series circuits have the same current running through each component in the circuit.

Parallel Circuit

A parallel circuit contains more than one path for current to pass through. In cases where there are different components along these separate paths, the strength of the current will vary. The voltage drop across each branch, however, is the same.

The equivalent resistance in a parallel circuit is equal to:

\[\frac{1}{R_{eq}} = \frac{1}{R_1} + \frac{1}{R_2} + …\]

where \(R_{eq}\) is the equivalent resistance, \(R_1\) is the first resistor, \(R_2\) is the second resistor, etc.

Unlike a series circuit, in a parallel circuit, if one branch is disconnected from the circuit, the current will continue to pass through the remaining branches.

Series-Parallel Circuit

Not all resistor circuits are simple series or parallel arrangements. Many are combinations of parallel resistors connected in series with other resistors or combined with other parallel resistor groups. These are described as series-parallel circuits. The simplest approach to analyzing a series-parallel circuit is to resolve each series-connected group of resistors into its equivalent resistance and each parallel-connected group into its equivalent resistance. The process is repeated as many times as necessary.

Electrical Power

Electrical power is a quantitative measurement of the amount of work that can be done by a circuit per unit of time. The formulas that can be used to calculate the electric power generated or dissipated are:

\[P = V \cdot I\] \[P = R \cdot I^2\] \[P = \frac{ V^2}{ R}\]

where P is power, V is voltage, R is resistance, and I is current.

In a circuit, power is generated by a voltage source, and loads dissipate it.

Electrical Units of Measurement:

Ohms—measure resistance: ohm = volt per amp

Amperes—measure current: amp = coulomb per second

Volts—measure voltage: volt = (newton x meter) per coulomb

Watts—measure power: watt = joule per second

Metric Prefixes—nano- is \(1 \cdot 10^{-9}\), micro- is \(1 \cdot 10^{-6}\), milli- is \(1 \cdot 10^{-3}\), centi- is \(1 \cdot 10^{-2}\), kilo- is \(1 \cdot 10^3\), mega- is \(1 \cdot 10^6\), and giga- is \(1 \cdot 10^9\)