To begin our study of electronics, we’ll start to get familiar with
some common electrical components, and with some common instruments that
technicians use to make measurements. We’ll also see that technicians
must understand a number of electrical quantities, and
they must know what units these quantities are measured
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.
Electrical and Electronic Components
If you look inside an electronic device such as a computer or a telephone,
you’ll see a large of number of electrical parts, or components.
These components include resistors, capacitors, inductors, transformers,
and semiconductor devices.
Resistors are components that limit the amount of
electrical current in a circuit. These are probably the most common
type of electrical component.
Here is a photograph of a resistor from Sinclair’s labs, shown next
to a quarter to give you an idea of its size.
Capacitors are components that store electrical
charge. Another way of saying this is that they store energy in an
electric field. Capacitors are also widely used to block direct current
(dc) and pass alternating current (ac).
Here are some photos of capacitors found in Sinclair’s labs. First,
here are two ceramic capacitors:
The next photgraph shows three plastic-film capacitors:
Finally, here are three electrolytic capacitors:
Inductors are components that store energy in a
magnetic field (as opposed to an electric field). Inductors are widely
used in filters and in many other applications.
Here is a photo of some inductors found in Sinclair’s labs.
Transformers are components that increase or decrease the voltage
in a circuit.
Here are two photos of transformers from our labs.
The components discussed above are referred to as electrical
components. Modern devices such as computers and radios
also contain many electronic components. Most electronic
components are made of a semiconductor material, such as silicon.
Semiconductor devices includes diodes, transistors, integrated circuits,
and several other kinds.
In this course and later courses you’ll use a variety of components.
The sooner you learn to recognize components by sight, the better.
If you’re studying this e-Lesson in one of Sinclair’s electronics
labs, go right now to the cabinet containing components and find examples
of resistors, capacitors, inductors, transformers, and other components.
Use the pictures given above to identify the components.
Then take this self-test quiz to see if you can recognize the different
types of components.
the Self-Test icon to check your understanding.
Technicians use a variety of instruments to test and troubleshoot
circuits. Some common instruments are dc power supplies, function generators,
digital multimeters, and oscilloscopes.
DC Power Supply
A dc power supply is an instrument that produces
direct-current (dc) voltages and currents.
In Sinclair’s labs, dc power supplies are built into the digital-analog
trainers that you will use in many of your courses. A digital-analog
trainer combines several instruments into one piece of equipment. Here
is a photo of the digital-analog trainers found in our labs:
Here is a close-up photo of the controls for the dc power supply
contained in the trainer:
A function generator is an instrument that produces
alternating-current (ac) voltages and currents.
In Sinclair’s labs, a function generator is built into the digital-analog
trainer, which was pictured just above. Here
is a close-up photo of the controls for the trainer’s function generator
(click the photo for a larger picture):
Our labs also have standalone function generators such as this Tektronix
model CFG250 (click for a larger picture):
A digital multimeter (or DMM) is
an instrument used to measure voltage, current, or resistance.
Sinclair’s labs are equipped with several types of DMM’s, including
the Fluke model 8050 shown here:
and the Tektronix model CDM250 shown here:
Shown below is an inexpensive handheld DMM.
An oscilloscope is an instrument that is used to
display graphs of quickly changing voltages.
Sinclair’s labs are equipped with several types of oscilloscopes,
including the Tektronix model 2213 shown here:
An LCR meter is used to measure values of inductance,
capacitance, or resistance.
Other names for this meter include impedance meter, Z
meter, and inductor-capacitor analyzer.
Sinclair’s labs are equipped with several types of LCR meters, including
the Global Specialties model 3200 shown here:
and the Tegam model 253 shown here:
Another instrument that we’ll use later in this course is a frequency
counter, which is used to measure frequencies of ac voltages.
Sinclair’s labs are equipped with several types of frequency counters,
including the Tektronix model CFC250 shown here:
In this course and later courses you’ll use a variety of electronic
instruments. The sooner you learn to recognize instruments by sight,
If you’re studying this e-Lesson in one of Sinclair’s electronics
labs, go right now to the lab bench and find examples of digital-analog
trainers, function generators, multimeters, oscilloscopes, and LCR
meters. Use the pictures given above to identify the instruments.
Then take this self-test quiz to see if you can recognize the different
types of instruments.
Up to this point we have looked at several examples of components
and instruments. Those are all physical objects that you can hold in
A technician must also understand and know how to measure many different electrical
quantities. These are concepts, not physical objects. Common
examples of electrical quantities are voltage, resistance, and current.
We use italic letters as symbols to represent electrical quantities.
V is the symbol for voltage;
R is the symbol for resistance;
I is the symbol for current. Why I instead of C?
Because C is used as the symbol for another electrical quantity,
and we wouldn’t want to use the same symbol to represent two different
Each electrical quantity has a unit in which it
For example, current is measured in amperes, or, to say the
same thing in another way, the ampere is the unit of measure for
current. A particular current might have a value of 5 amperes.
Here’s an everyday, non-electrical example of this idea of units.
Think about the quantity called weight. Weight is measured in pounds,
or, to say the same thing in another way, the pound is the unit
of measure for weight.
Just as we have a symbol to represent each electrical quantity, we
also have a symbol to represent each electrical unit. Usually the symbols
for units are plain, non-italicized letters.
For instance, the symbol for the ampere is A. So to show that a
particular current is equal to 5 amperes, we would write I = 5 A.
Table of Electrical Quantities and Units
The table below lists some important
electrical quantities, along with their units and the corresponding
symbols. You must memorize the information in this table.
Symbol for the Unit
If you look closely, you will notice that the symbols for most quantities
are written with italicized letters, such as I or V.
But the symbols for most units are written with plain, non-italicized
letters, such as A or V. This is the standard, accepted way of doing
The symbols for some quantities and some units are letters
from the Greek alphabet. The only example in the table above is the
Electrical-Units Matching Game
By the end of this course you’ll need to memorize which units go
with which quantities.
I know it takes a while to memorize things like this, so don’t
panic! You’ll have plenty of time before anyone expects you to remember
all of these terms and symbols. But the sooner you start learning
the language that technicians and engineers use to communicate with
each other, the better off you’ll be.
For this week’s lab, the three rows of the table that you’ll want
to remember are the rows for capacitance, inductance, and resistance.
To work on this skill, be sure to play the Electrical-Units
Matching Game. Like all of the games on the Games page,
this one 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!
The game will teach you a few more units that aren’t listed
in the table above. You won’t need to learn those for this course,
but you’ll use them in later courses.
Again, I don’t expect you to learn all of these terms and symbols
immediately. Come back to these games throughout the quarter to keep
Relating Components to Quantities
Let’s take a closer look at three of the components mentioned earlier
(resistors, capacitors, and inductors), and see how these components
relate to some of the quantities we’ve just been discussing.
More About Resistors
Earlier we said that resistors are components that limit the amount
of electrical current in a circuit, and we showed this photograph of
Now we can add to our earlier definition by noting that every resistor is
manufactured to have a specific amount of the electrical quantity called resistance.
Recall from the table above that the
symbol for resistance is R, and that resistance is measured
in ohms, and that the symbol for ohms is Ω. We’ll use these symbols
frequently when discussing resistors.
For example, suppose that a particular resistor has a resistance
value of 200 ohms. We would write this as:
R = 200 Ω
Typical resistance values for resistors range from 10 Ω (a
small resistance) to 10,000,000 Ω (a large resistance).
In the photo above, note the colored bands on the resistor’s body.
These colors indicate the resistor’s value in ohms. We’ll learn how
to "read" these colors in Unit 2 of this course. (If you
want to get a head start on this topic, a good way to do it would be
to read the "Study" section of the Color-Code
Matching Game and then play the game until you can remember which
number each color stands for.)
More About Capacitors
Earlier we said that capacitors are components that store electrical
charge, and we showed several photos of capacitors, including this
Now we can add to our earlier definition by noting that every capacitor is
manufactured to have a specific amount of the electrical quantity called capacitance.
From the table above we see that the
symbol for capacitance is C, and that capacitance is measured
in farads, and that the symbol for farads is F. We’ll use these symbols
frequently when discussing capacitors.
For example, suppose that a particular capacitor has a capacitance
value of 1 farad. We would write this as:
C = 1 F
Typical capacitance values for capacitors range from 0.0000000001 F
(a small capacitance) to 0.001 F (a large capacitance).
In the photo above, note the numbers on the larger capacitor’s body.
These numbers indicate the capacitor’s value in farads. We’ll learn
how to interpret these numbers in Unit 2.
More About Inductors
Earlier we said that inductors are components that store energy in
a magnetic field, and we showed this photograph of some inductors:
Now we can add to our earlier definition by noting that every inductor is
manufactured to have a specific amount of the electrical quantity called inductance.
Our table of quantities tells us that
the symbol for inductance is L, and that inductance is measured
in henries, and that the symbol for henries is H. We’ll use these symbols
frequently when discussing inductors.
For example, suppose that a particular inductor has an inductance
value of 1 henry. We would write this as:
L = 1 H
Typical inductance values for inductors range from 0.0000001 H
(a small inductance) to 1 H (a large inductance).
In the photo above, note the numbers on the left-hand inductor’s
body. These numbers indicate the inductor’s value in henries. We’ll
learn how to interpret these numbers in Unit 2.
Prefixes for Large or Small Numbers
When discussing resistances, capacitances, inductances, and other
electrical quantities, we must often deal with very large numbers (in
the thousands or millions, or even larger) and with very small numbers
(thousandths or millionths, or even smaller).
To avoid having to write lots of zeroes when dealing with large or
small numbers, we’ll use some standard prefix letters as abbreviations.
For example, we know that resistance is measured in units called
ohms (abbreviated Ω). But many resistances have values in
the thousands of ohms or millions of ohms, and for such large values
it’s convenient to use larger units called kilohms (abbreviated kΩ)
or megohms (abbreviated MΩ).
Also, we know that capacitance is measured in units called
farads (abbreviated F). But many capacitances have values
much smaller than one farad, and for such small values it’s convenient
to use smaller units called picofarads (abbreviated
or nanofarads (abbreviated nF) or microfarads (abbreviated
Likewise, inductance is measured in units called
henries (abbreviated H). But since many inductances have values
much smaller than one henry, it’s often convenient
to use smaller units called microhenries (abbreviated
µH) or millihenries (abbreviated mH).
In Unit 2 we’ll discuss the prefixes k, M, p, n, µ, and m in
more detail. We’ll see, for instance, that 1 MΩ is just
a shorthand way of writing 1,000,000 Ω, and that 1 µF
is just a shorthand way of writing 0.000001 F. For now, you should
simply be aware that an expression such as
C = 330 pF
is a shorthand way of writing a very large or very small number without
having to write a lot of zeroes.
Nominal Values and Tolerances
Suppose you’re building an electronics project that requires a 220 Ω resistor.
(Remember, this means a resistor whose resistance is equal to 220 ohms.)
So you go to the nearest Radio Shack store and ask the clerk for a
resistor of that size. The clerk will be happy to sell you such a resistor,
but will the resistor’s value be exactly 220 Ω? Probably
not. It will probably be a little higher (maybe 224 Ω) or
a little lower (maybe 213 Ω), but it will be close enough
to 220 Ω that your project should work correctly when you
In this example we would say that 220 Ω is the resistor’s nominal
value, which means the value that the manufacturer was shooting
for when they manufactured that resistor. But the resistor’s actual
value will probably be somewhat higher or lower than the
How far away from the nominal value can the actual value be? To
quantify this, manufacturers use tolerance ratings.
When you buy that resistor at Radio Shack, you might have your choice
of buying a resistor with a 5% tolerance, or one with a 10% tolerance,
or one with a 20% tolerance. This tolerance rating tells you how far
from the nominal value the actual value may be.
So if you buy one with a 5% tolerance rating, then the manufacturer
is guaranteeing you that the resistor’s actual value will be within
5% of 220 Ω.
The same ideas apply to other components as well. If you buy a 470 pF
capacitor or a 15 mH inductor, those numbers represent the nominal
values of the components. The actual values will probably be higher
or lower, but the tolerance ratings will tell you how close to the
nominal values you can expect the actual values to be.
Tolerance ratings are almost always given as percentages, such as
5% or 10%. You’ve probably studied percentages at some time in a math
class, but let’s do a quick review.
The main thing to remember about percentages is that they just involve
moving a number’s decimal point over by two places.
Example: writing 5% is just a fancy way of writing the number 0.05.
So, to use an example involving money, if somebody asks you to find
5% of $750, the answer is $37.50, since
0.05 × $750 = $37.50
Your calculator may have a % key, in which case you could solve that
problem by typing in
5% × 750 =
but when you type that in, your calculator simply changes 5% to 0.05
and then does the multiplication.
Now let’s talk more about the math involved in tolerance ratings.
In particular, if you know a component’s nominal value and its tolerance
rating, then you should be able to figure out the range of actual values
that the component might have.
We’ll use a 220 Ω resistor with 5% tolerance as an example.
To find a resistor’s tolerance in ohms, multiply its nominal value
by the percentage tolerance.
Example: For a 220 Ω resistor with 5% tolerance, the
tolerance in ohms is 11 Ω, since
.05 × 220 Ω = 11 Ω.
To find the minimum value that the resistor can have, subtract its
tolerance in ohms from its nominal value.
In the example above, the minimum possible value is 209 Ω,
220 Ω − 11 Ω = 209 Ω.
To find the maximum value that the resistor can have, add its
tolerance in ohms to its nominal value.
In the example above, the maximum possible value is 231 Ω,
220 Ω + 11 Ω = 231 Ω.
Therefore, if you buy a 220 Ω resistor with a 5% tolerance
rating, the manufacturer is guaranteeing you that the resistor’s actual
value will be between 209 Ω and 231 Ω.
Unit 1 Review
This e-Lesson has covered some important topics, including:
some common electronic components
some common electronic instruments
a list of electrical quantities, along with their units of measurement
resistors, capacitors, and inductors
some prefixes for large and small numbers (M, k, m, µ,
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.