Electronics Information Study Guide for McGraw-Hill's ASVAB (page 2)
Practice problems for this study guide can be found at:
ASVAB Electronics Information Questions
The electronics information questions that appear on the ASVAB measure how much you understand about electricity, electric circuits, and electrical and electronic devices and systems.
The questions may ask you to identify a particular device on a circuit diagram, explain how to measure voltage or current, or identify particular types of circuits. If you have tinkered with electricity or electronics at home or in school, you may be familiar with some of the topics covered here.
Whichever ASVAB version you take, you'll have only about half a minute to answer each electronics information question, so you'll have to work fast if you want to get a good score. That's why it pays to spend time studying the test topics and tackling plenty of sample ASVAB Electronics Information questions. The topic review that follows will help prepare you to answer ASVAB Electronics Information questions.
At the end of the chapter there is a short quiz with questions modeled on those on the actual test. Read carefully through the review materials in this chapter, then use the quiz to find out how well you have mastered this subject area. Go back and reread the review materials for any quiz items you miss.
Let's start by getting acquainted with some basic concepts in electricity. To understand electricity, you need to know the following:
- Electricityis a form of energy that can travel invisibly through conductors. It can be used in so many ways that we could call it the most versatile form of energy. Electricity is carried by moving charged particles, especially by electrons. Electrons are tiny negative charges that orbit the nucleus of an atom.
- A conductoris a material that allows an easy flow of electrons. Silver, copper, and aluminum are all good conductors.
- An insulatoris a material that resists the flow of electrons. Rubber, plastic, and ceramic are good insulators.
- A circuitis a loop of conductor that takes electricity from its source to the load (the place where it does some work) and back to the source.
- A loadis anything in the circuit, such as a heater, a light, or a motor, that uses power.
- Direct current(DC) is a steady-flowing type of electricity, produced by batteries and used in flashlights, boom boxes, and computers.
- Alternating current(AC) is a type of current that changes direction many times per second. AC is used in home wiring, mainly because it can be transported long distances over transmission wires.
- Electronicsis a branch of science that deals with complicated uses of electricity, such as in radios, televisions, and computers.
To understand electricity, you also need to know a few technical terms. Study the following list.
- Electric currentis the amount of electrons flowing through a conducting material.
- Electric poweris the amount of power consumed by an electrical device.
- Voltageis a force that affects the rate at which electricity flows through a conductor. It is sometimes called electrical pressure. The higher the voltage, the more likely electricity is to "leak" across an insulator or an air gap. That's one reason higher voltages are more dangerous. Voltage droptells how much electrical pressure is used in a part of the circuit.
- Frequencyis the number of complete alternations— from one direction to the other and then back again—that alternating current makes per second. Each complete alternation is called a cycle.
- Resistanceis the opposition of a material to the flow of electricity through it. All circuits must have a resistance. If they don't, they are called short circuits, and wires can overheat.
Units of Measure and Measuring Devices
Different aspects of electricity are measured using different units of measure. Special measuring devices are used. The following table shows the different units and devices.
Ohm's law describes the relationship among electrical pressure (voltage), current strength (amperage), and resistance (ohms) in any circuit:
If you know two of these three quantities, you can always calculate the third.
Here's an easy way to remember how to use Ohm's law to find the third quantity if you know two already. On the circle (below), place your finger over the quantity you want to find. Look at the remaining two quantities to see how to calculate the third quantity.
Memorize the equations on the circle; you'll need them on the ASVAB. Let's look at a couple of examples of how to use the Ohm's law circle.
Find the amperes if a 120-volt current runs through 6 ohms.
Amperes = volts/ohms
Amperes = 120/6 = 20 amperes
Or cover ohms in the circle. Notice that what remains is volts divided by ohms (the same result you would get by remembering the three formulas above).
Amperes = 120/6 = 20 amperes
In a 6-volt circuit with 24 amperes flowing, what is the resistance?
Ohms = volts/amperes
Ohms = 6/24 = 1/4 ohms
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