EET 155 Unit 1: EET 150 Review and Electromagnetism

Unit 1: Review and Electromagnetism

To get started, we'll review some material that you studied in two earlier courses: EET 114 (Basic Electronic Measurements) and EET 150 (DC Circuits).

After this review , we'll discuss the close relationship between electricity and magnetism. Many common and useful devices, such as solenoids and loudspeakers, rely on the fact that electricity can be used to produce magnetism. Many other common devices, such as electrical generators, rely on the fact that magnetism can be used to produce electricity. For a detailed treatment of these topics, you should read the following sections of Thomas Floyd's Principles of Electric Circuits (8th edition):

Magnetism and Electromagnetism (Chapter 10)

But also realize that the textbook provides more detail on these topics than we'll need for this course. So don't get bogged down in the chapter's equations or discussion of physics. The e-Lesson below reviews the main points of the reading assignment, and also gives some information not found in the reading. Most important of all, it contains Self-Test questions to give you some practice using what you've read about.

After you finish the e-Lesson, you'll be ready to take Quiz #1, perform Lab #1, and do Homework #1.

E-LESSON:

For any topic below with a Self-Test icon (which looks like this ), click the icon to test your understanding of that topic. Self-Tests are for your practice only; no grades are recorded. The questions will appear in a new window. You may wish to resize this window so that you can read the questions more easily; then close the window when you're finished with the questions for that topic.

EET 114/EET 150 Review

Here is a list of the main topics that we'll review from EET 114 and EET 150:
- Ohm's law
- energy and power
- series circuits
- parallel circuits
- series-parallel circuits
- circuit theorems.
Read on for a review of these topics.

Ohm's Law (Chapter 3 of Floyd's book)

Unit 5 of EET 114 covered the following topics:
- Ohm's law
- estimation
- series-parallel circuits.
To see how well you remember these topics, take the following self-test:
If you'd like to review this material, work through the entire e-Lesson for Unit 5 of EET 114.

Energy and Power (covered in Chapter 4 of Floyd's book)

Unit 6 of EET 114 covered the following topics:
- energy and power
- resistor power ratings
- power supplies and efficiency.
To see how well you remember these topics, take the self-test by clicking the icon below:
If you'd like to review this material, work through the entire e-Lesson for Unit 6 of EET 114

Series Circuits (Chapter 5 of Floyd's book)

Unit 2 of EET 150 covered the following topics:
- series connections and series paths
- series circuits
- voltage drops and voltage rises
- voltage sources in series
- Kirchhoff's Voltage Law (KVL)
- voltage dividers and the voltage-divider rule
- power in series circuits
- open circuits and short circuits.
To see how well you remember these topics, take the self-test by clicking the icon below:
If you'd like to review this material, work through the entire e-Lesson for Unit 2 of EET 150.

Parallel Circuits (Chapter 6 of Floyd's book)

Unit 3 of EET 150 covered the following topics:
- parallel connections and parallel circuits
- Kirchhoff's Current Law (KCL)
- total resistance of resistors in parallel
- parallel-connected sources
- current-divider rule
- power in parallel circuits
- shorts and opens in parallel circuits.
To see how well you remember these topics, take the self-test by clicking the icon below:
If you'd like to review this material, work through the entire e-Lesson for Unit 3 of EET 150.

Series-Parallel Circuits (Sections 7-1 and 7-2 of Floyd's book)

Unit 4 of EET 150 covered the following topics:
- identifying series and parallel relationships
- analyzing series-parallel circuits
- power in series-parallel circuits
- ground symbol and bubble symbol.
To see how well you remember these topics, take the self-test by clicking the icon below:
If you'd like to review this material, work through the entire e-Lesson for Unit 4 of EET 150.

More Series-Parallel Circuits (Sections 7-3 through 7-7 of Floyd's book)

Unit 5 of EET 150 covered the following topics:
- loaded voltage dividers
- voltmeter loading
- ladder networks
- the Wheatstone bridge
- troubleshooting series-parallel circuits.
To see how well you remember these topics, take the self-test by clicking the icon below:
If you'd like to review this material, work through the entire e-Lesson for Unit 5 of EET 150.

Circuit Theorems (Sections 8-1 through 8-4 of Floyd's book)

Unit 6 of EET 150 covered the following topics:
- practical voltage sources
- practical current sources
- source conversion
- the superposition theorem.
To see how well you remember these topics, take the self-test by clicking the icon below:
If you'd like to review this material, work through the entire e-Lesson for Unit 6 of EET 150.

More Circuit Theorems (Sections 8-5 and 8-7 of Floyd's book)

Unit 7 of EET 150 covered the following topics:
- Thevenin's theorem
- the maximum power transfer theorem.
To see how well you remember these topics, take the self-test by clicking the icon below:
If you'd like to review this material, work through the entire e-Lesson for Unit 7 of EET 150.

Table of Electrical Quantities

The table below summarizes the electrical quantities that you studied in EET 150. The table shows the abbreviation for each quantity, along with the standard unit for measuring the quantity and the abbreviation for the unit.

Quantity	Abbreviation	Unit	Abbreviation for the Unit
charge	Q	coulomb	C
current	I	ampere	A
voltage (or emf)	V (or E)	volt	V
resistance	R	ohm	Ω
conductance	G	siemens	S
energy (or work)	W	joule	J
power	P	watt	W
efficiency	η
capacitance	C	farad	F
time constant	τ	second	s
inductance	L	henry	H

If you look closely, you will notice that the abbreviations of the quantities are written with italicized letters (such as Q and I). But the abbreviations of the units are written with plain, non-italicized letters (such as C and A). This is the standard, accepted way of doing things. Our textbook (along with other books) follows this rule, and you should too when you use these abbreviations in a typed paper or lab report.
In this course we'll learn quite a few new quantities, and this table will grow. Unit 3 will present an expanded version of the table.

Electronics Games

I've written some games to help you develop your electronics skills. Each game has a Study mode that reviews the theory, a Practice mode that lets you practice with no time pressure, and a Challenge mode that tests your skill while the clock is running. If you're fast, you may even get your name on the high-score board!
For further review of some of the skills you learned in EET 150 (or in EET 114), play the following games:
This completes our review of material from EET 114 and EET 150. Let's move on now to some new material.

Permanent Magnets (Floyd, p. 371)

Permanent magnets, like the kind you probably have hanging on your refrigerator, keep their magnetic properties for a long time.
One end of a magnet is called its north (N) pole and the opposite end is called its south (S) pole.
When two magnets are placed near each other, opposite poles attract, and like poles repel.

Magnetic Fields (Floyd, p. 371)

If you stop and think about it, it's surprising that one magnet can push or pull another magnet when they're not touching each other. How can that happen?
To explain this fact, it's useful to think of a magnet as being surrounded by a magnetic field, which carries the force that it exerts on other magnets. So even when two magnets aren't directly touching each other, they can still affect each other indirectly through their magnetic fields.
We draw the magnetic field as lines leaving the magnet's north pole and entering the south pole.
These imaginary lines are called flux lines.
Scientists have developed a complete theory of magnetic fields. This theory defines measurable quantities such as magnetic flux and magnetic flux density, and it derives mathematical equations that relate these quantities to each other. The textbook discusses some of these equations, but for this course you won't need to study them.

Electromagnetism (Floyd, pp. 375-379)

Today we know that electricity and magnetism are very closely related. But nobody realized this until the 1800's.
In 1820, Hans Oersted discovered that electrical current creates a magnetic field. This phenomenon is called electromagnetism.
Again, scientists have developed a detailed theory of electromagnetism that involves lots of new terms (such as permeability, reluctance, and magnetomotive force) and equations. You won't need to know these concepts for this course, but you might want to skim Section 10-2 in the textbook for an overview.

Applications of Electromagnetism (Floyd, pp. 381-387)

Electromagnetism (using electricity to create magnetism) has many, many practical applications. A few devices that use electromagnetism are electric motors, loudspeakers, relays, antennas, and solenoids. Section 10-3 in the textbook gives good explanations of how some of these devices work.

Electromagnet (Floyd, p. 380)

Many of the devices just mentioned contain electromagnets. An electromagnet displays magnetic properties only when current is passing through it. So you can think of it as a magnet that you can turn on or off. This is different from a permanent magnet, which you can't "turn off."
Electromagnets are constructed simply by wrapping wire around a core, which is just a rod or bar usually made of an iron alloy. When you pass current through that wrapped-up wire, the whole thing behaves like a magnet. When you stop passing current through the wire, it stops behaving like a magnet.

An Animated Lesson from our Friends in Wisconsin

Instructors in the Wisconsin Technical College System have created a library of short online animations and quizzes to help students learn electronics. I'll include links to some of these "learning objects." Whenever you see the icon below, click it to see a learning object on the material you're studying. The Wisconin learning object will open in a new window; close the winow when you're finished and want to return to this lesson.
This first one will tell you more about electromagnets. Click the icon now.

Turns and Windings

In an electromagnet, each complete wrap of wire around the core is called a turn, and all of the turns taken together are called a coil or a winding.

Solenoid (Floyd, p. 381)

A solenoid is an electromagnetic device in which an electrical signal is used to control the position of a metal rod called a plunger. Solenoids are widely used in valves that control the flow of liquids and gases. They're also used in other applications, such as the locks in car doors.

Relay (Floyd, p. 382)

A relay is an electromagnetic device in which an electrical signal in one circuit is used to close or open a switch, thus either completing or breaking another electric circuit. Typically the first circuit (called the control circuit) is a low-voltage, low-current circuit, often containing a pushbutton that an operator can press. And in many cases the other circuit is a high-voltage, high-power circuit. So we have a low-voltage circuit being used to control the operation of a high-voltage circuit. This arrangement provides safety benefits, since it lets the human operator control the high-voltage circuit without having to touch any switches that carry dangerously high currents.

Electromagnetic Induction (Floyd, pp. 390-392)

As mentioned above, Oersted realized in 1820 that every electrical current creates a magnetic field. (That's called electromagnetism.) A few years later, Michael Faraday realized that this works in the opposite direction too: you can use magnetic fields to create electricity. This is called electromagnetic induction.
In particular, Faraday found that if you move a wire through a magnetic field, you'll create a voltage across the ends of the wire. We say that a voltage is induced across the wire.
- A voltage can also be induced by moving the magnetic field past a wire that is at rest.
In both of these cases, the important thing is that the wire's motion or the field's motion results in a changing magnetic field in the vicinity of the wire. In fact, a voltage is induced whenever there's a change in the size of the magnetic field surrounding a wire, even if the wire and the magnetic field are both at rest.
In all of these cases, the induced voltage will be greater if you use a coil of wire rather than a straight piece of wire. So most devices that rely on electromagnetism contain coils.

Faraday's Law (Floyd, p. 392)

The basic law of electromagnetism is called Faraday's law. It can be written as an equation, or stated in words.
Stated in words, it says that the voltage induced across a coil of wire equals the number of turns in the coil times the rate of change of the magnetic flux.

Applications of Electromagnetic Induction (Floyd, pp. 394-397)

Electromagnetic induction has many practical applications. Perhaps the most important practical application is the electrical generator, which creates electricity by rotating a coil of wire between the two ends of a magnet.
Read Section 10-6 in the textbook for a good explanation of how a DC generator works. AC generators work in a similar way. Take a look at the following learning object for a basic explanation.
Another interesting application is the metal detector, which is explained in this learning object:

Unit 1 Review

This e-Lesson has covered several important topics, including:
- a review of material from EET 150
- electromagnetism
- electromagnetic induction.
To finish the e-Lesson, take this self-test to check your understanding of these topics.

Congratulations! You've completed the e-Lesson for this unit. What's next?

Take the Practice Quiz to see how the quiz tool works, and then take Quiz #1.
Perform Lab #1. This is not a graded lab, so you don't need to turn in anything for it.
Do Homework #1.
For more practice with the material from this unit, visit the textbook's Chapter 10 web page and take the multiple-choice, true/false, circuit-analysis, and fill-in-the-blank quizzes provided there.
Keep practicing your skills by playing the games on the Games page.
Prepare for Unit 2 by reading Sections 12-1 through 12-5 and Sections 13-1 through 13-5 of Thomas Floyd's Principles of Electric Circuits (8th edition).

Then you'll be ready to go on to Unit 2.

Nick Reeder | Electronics Engineering Technology | Sinclair Community College

Send comments to nick.reeder@sinclair.edu