Unit 1:
Review and Electromagnetism
To get started, we'll review some
material that you studied in EET 1150 (D.C. 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 any topic below with a SelfTest icon (which looks like this ),
click the icon to test your understanding of that topic. SelfTests 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 1150 Review
 Here is a list of the main topics that we'll review from EET 1150:
 Ohm's law
 energy and power
 series circuits
 parallel circuits
 seriesparallel circuits
 circuit theorems
 capacitors and inductors in D.C. circuits.
 Read on for a review of these topics.
Ohm's Law
 Unit 5 of EET 1150 covered the following topics:
 Ohm's law
 estimation
 seriesparallel circuits.
 To see how well you remember these topics, take the following selftest:
 If you'd like to review this material, work through the entire eLesson
for Unit 5 of EET 1150.
Energy and Power
 Unit 6 of EET 1150 covered the following topics:
 energy and power
 resistor power ratings
 power supplies and efficiency.
 To see how well you remember these topics, take the selftest by
clicking the icon below:
 If you'd like to review this material, work through the entire eLesson
for Unit 6 of EET 1150
Series Circuits
 Unit 7 of EET 1150 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 voltagedivider rule
 power in series circuits
 open circuits and short circuits.
 To see how well you remember these topics, take the selftest by
clicking the icon below:
 If you'd like to review this material, work through the entire eLesson
for Unit 7 of EET 1150.
Parallel Circuits
 Unit 8 of EET 1150 covered the following topics:
 parallel connections and parallel circuits
 Kirchhoff's Current Law (KCL)
 total resistance of resistors in parallel
 parallelconnected sources
 currentdivider rule
 power in parallel circuits
 shorts and opens in parallel circuits.
 To see how well you remember these topics, take the selftest by
clicking the icon below:
 If you'd like to review this material, work through the entire eLesson
for Unit 8 of EET 1150.
SeriesParallel Circuits
 Unit 9 of EET 1150 covered the following topics:
 identifying series and parallel relationships
 analyzing seriesparallel circuits
 power in seriesparallel circuits
 ground symbol and bubble symbol.
 To see how well you remember these topics, take the selftest by
clicking the icon below:
 If you'd like to review this material, work through the entire eLesson
for Unit 9 of EET 1150.
More SeriesParallel Circuits
 Unit 10 of EET 1150 covered the following topics:
 loaded voltage dividers
 voltmeter loading
 ladder networks
 the Wheatstone bridge
 troubleshooting seriesparallel circuits.
 To see how well you remember these topics, take the selftest by
clicking the icon below:
 If you'd like to review this material, work through the entire eLesson
for Unit 10 of EET 1150.
Circuit Theorems
 Unit 11 of EET 1150 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 selftest by
clicking the icon below:
 If you'd like to review this material, work through the entire eLesson
for Unit 11 of EET 1150.
More Circuit Theorems
 Unit 12 of EET 1150 covered the following topics:
 Thevenin's theorem
 the maximum power transfer theorem.
 To see how well you remember these topics, take the selftest by
clicking the icon below:
 If you'd like to review this material, work through the entire eLesson
for Unit 12 of EET 1150.
Capacitors in DC Circuits
 Unit 13 of EET 1150 covered the following topics:
 capacitance
 charge and voltage on a capacitor
 capacitor specifications
 types of capacitors
 capacitors in series, in parallel, and in seriesparallel
 DC RC circuits
 calculating initial values, steadystate values, and transient
values in DC RC circuits
 time constant of a DC RC circuit.
 To see how well you remember these topics, take the selftest by
clicking the icon below:
 If you'd like to review this material, work through the entire eLesson
for Unit 13 of EET 1150.
Inductors in DC Circuits
 Unit 14 of EET 1150 covered the following topics:
 inductance
 types of inductors
 energy stored in an inductor
 inductors in series, in parallel, and in seriesparallel
 calculating initial values, steadystate values, and transient
values in a DC RL circuit
 time constant of a DC RL circuit.
 To see how well you remember these topics, take the selftest by
clicking the icon below:
 If you'd like to review this material, work through the entire eLesson
for Unit 14 of EET 1150.
Table of Electrical Quantities
 The table below summarizes the electrical quantities that you studied
in EET 1150. 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, nonitalicized
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 2 will present an expanded
version of the table.
Electronics Games
 For further review of some of the skills you learned in EET 1150,
play the following games. 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 highscore board!
 This completes our review of material from EET
1150. Let's move on now to some new material.
Permanent Magnets
 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
 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. For this course you won't need to study
them.
Electromagnetism
 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.
Applications of Electromagnetism
 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.
Electromagnet
 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 wrappedup 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
 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
 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 lowvoltage, lowcurrent circuit, often containing
a pushbutton that an operator can press. And in many cases the other
circuit is a highvoltage, highpower circuit. So we have a lowvoltage
circuit being used to control the operation of a highvoltage
circuit. This arrangement provides safety benefits, since it lets the
human operator control the highvoltage circuit without having
to touch any switches that carry dangerously
high currents.

Electromagnetic Induction
 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
 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
 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.
 Take a look at the following lesson for a basic explanation
of how a generator works.

 Another interesting application is the metal detector, which is
explained in this lesson:

Unit 1 Review
 This eLesson has covered several important topics, including:
 a review of material from EET 1150
 electromagnetism
 electromagnetic induction.
 To finish the eLesson, take this selftest to check your understanding
of these topics.

Congratulations! You've completed the eLesson for this unit.