Download A Virtual Circuits Lab - National Science Teachers Association

Building students’
understanding of series,
parallel, and complex circuits
C
Matthew E. Vick
ircuits are at the heart of cell phones, gaming systems, and even that old lamp in your room. Teaching about circuits can help students understand the
underlying principles of many of today’s electronic
devices and require them to use quantitative thinking skills.
The University of Colorado’s Physics Education Technology (PhET) website (see “On the web”) offers free, highquality simulations of many physics experiments that can
be used in the classroom. The Circuit Construction Kit, for
example, allows students to safely and constructively play
with circuit components while learning the mathematics
behind many circuit problems. This article describes my
experience using the Circuit Construction Kit with my 11ththrough 12th-grade physics students.
S i m u l at i o n s vs . h a n d s - o n l a b s
Building circuits often entails the use of breadboards (a
construction base for an electronic circuit). Although breadboards present a tactile opportunity for physics students, their
use is not always well understood. This is often because the
physical layout of resistors (see photo, p. 30) does not look
much like the diagrams students draw in class. Also, students
who fail to measure current in series often blow the multimeter’s fuses. This adds stress for both students and the teacher,
who must continually replace these devices.
Finkelstein and colleagues (2005) studied the effects of
using the PhET Circuit Construction Kit in place of a traditional circuit-building lab in a college-level introductory
physics course. They found that students who used these
simulations scored higher on a conceptual set of circuit
questions and built physical circuits faster than students who
participated in a traditional hands-on lab. Teaching assistants
reported that the simulations allowed students to focus on
content questions rather than the mechanical questions that
result from blown fuses or loose connections. I have found the
same to be true in my physics classes: The PhET simulations
allow me to focus on the inquiry elements of the lab, rather
than the mechanics of circuit construction.
Finkelstein and colleagues (2006) also indentify several
characteristics that the simulations illustrate in correlation
with the National Science Education Standards (NRC 1996).
Content Standard A, for example, emphasizes that students
develop the “abilities necessary to do scientific inquiry” (NRC
1996, p. 173); using the PhET simulations, students draw
conclusions based on their own data. Content Standard B
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The Science Teacher
A Virtual Circuits Lab
encourages students to develop an
understanding of the “structure of
atoms” and “conservation of energy” (NRC 1996, p. 176); the PhET
simulations help students visualize Keywords: Electronic circuits
at www.scilinks.org
the invisible world of electrons and Enter code: TST051002
address the misconception that electrons are “used up” in a circuit.
The important thing to remember, though, is that the
simulations themselves do not make for a constructivist,
inquiry-based lesson—the teacher must use these simulations as a tool for exploration and discussion. Lessons should
allow for creativity and problem solving, instead of simple
observation.
A c i rc u i t s l e a r n i n g c yc l e
The PhET Circuit Construction Kit allows students to
create circuits that closely resemble schematic diagrams—
symbolic representations of the resistors, batteries, and
other items in a circuit. Creating circuits that resemble
schematic diagrams provides scaffolding for students to
connect the symbolic and physical worlds. I use the Atkin
and Karplus (1962) learning cycle in my physics class, which
can be adapted for other physical science courses. The cycle
consists of three stages: concept exploration, concept introduction, and concept application; the 5E Learning Cycle—
engage, explore, explain, elaborate, and evaluate—is a
similar model.
Before using the PhET Circuit Construction Kit with my
class, I have students physically connect a single resistor to an
adjustable voltage power supply. They then plot the voltage
versus the current to introduce the concepts of Ohm’s law and
resistance. This physical experience is the part of the lesson
designed to “hook” students. It also introduces Ohm’s law
in an inquiry-based manner.
The lesson then begins with three days of virtual “exploratory” activities that help students discover Kirchoff’s laws:
one day for series circuits, one for parallel circuits, and one
for complex circuits. Screenshots from the PhET website
help guide students through the construction process, but
many choose to “play” and build circuits on their own. These
students add additional components (e.g., switches) or items
(e.g., pencil or coin) from a virtual grab bag. I have found
this to be encouraging, as less confident physics students in
previous classes did not show interest in “playing around”
with the circuits.
After completing the virtual exploratories, students
physically build the circuits on breadboards. Several students
have remarked that this experience got them excited about
electronics. When class time is limited, I make sure
that students build at least one physical circuit so
that those who enjoy working with electronic
devices have the opportunity to do so. (Safety
I m p o r t a n t t e r m s a n d co n ce p t s .
Ammeter: An instrument used to measure the electric current in a circuit.
Breadboard: A construction base for an electric circuit (see photo, p. 30).
Current: A flow of electric charges through a conductor; measured with an ammeter.
Kirchoff’s laws: Rules for finding current and voltage
in a series or parallel circuit.
Multimeter: An electronic device used to measure
voltage, current, and resistance that combines several
measurement functions into one unit.
Noncontact ammeter: A bull’s-eye that is placed
over any area of a circuit to read its current.
Ohm’s law: The current through a conductor between
two points is proportional to the voltage across the
two points and inversely proportional to the resistance between the two points, or Current = voltage/
resistance or I = V/R.
Resistance: The property of a material that resists
the flow of electric charges through it.
Voltage: A measure of the difference in electric potential between two points in a space, material, or
electric circuit.
Voltmeter: A device used to measure the voltage in
an electric circuit.
note: Students should be reminded to keep the voltage reading on their power supply at 4 V or less and
asked not to touch uninsulated wires; safety glasses
are required for this activity.)
S e r i e s c i rc u i t e x p l o rat o r y
The lesson’s first exploratory requires the most class time,
since students are still learning how to use the PhET website
and Circuit Construction Kit. In this activity, students construct a virtual series circuit with three resistors. I provide
them with short written instructions to guide them through
the simulation, since previous classes complained
that they did not have enough support to use the
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Pa ra l l e l c i rc u i t s e x p l o rat o r y
The second virtual exploratory, on parallel circuits, moves
faster than the first since it “parallels” the format. It is important to include screenshots in the instructions for this activity
because the parallel circuits need “extra wire” to allow for the
measurement of current in each branch of the circuit. It is
also important that the resistance values are different so that
the current through each branch will also be different. This
helps avoid the misconception that current is always equal in
each branch of a parallel circuit.
Once again, students form their own data tables for voltage and current. I ask them to use the noncontact ammeter to
record the total voltage across the battery and the total current
right next to the battery. When measuring resistance, I have
students use Ohm’s law with the total voltage and current,
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The Science Teacher
Photo courtesy of the author
PhET site. Instructions for changing the default values of
the resistors are particularly important—this helps students
develop accurate generalizations. If all resistance values are
left at the default of 10 Ω, the voltage across each resistor
will be equal, which can lead to the misconception that
voltages across series resistors are always equal. The written
instructions for each exploratory activity and an application
lab can be found online (see the “Editor’s note” at the end
of this article).
The interface in the Circuit Construction Kit includes a
voltmeter with leads, so students can connect opposite sides
of the resistors with a power supply for measuring voltage.
Internal resistance and resistance in the wires are modeled
to make the simulation more realistic.
To measure current, students use either the ammeter or
the “noncontact ammeter,” a bull’s-eye that is placed over an
area of the circuit to read its current. I use the noncontact
ammeter to avoid the difficulty of “breaking” circuits when
inserting the ammeter. Other instructors may choose to use
the ammeter so that their students can model the skill of
inserting this device.
Students explore the lesson’s concepts by drawing conclusions from their data, instead of through open-ended circuit
building. The exploratory instructions I provide ask them to
construct a data table of voltages across and currents through
each of the resistors. Students share their data tables with the
class and discuss the concepts that voltage drops in one circuit
add up to the total voltage drop in an entire circuit and that
current is the same throughout a series circuit.
When using the Circuit Construction Kit, teachers should
be aware that the simulation shows the charges moving faster
with higher current. To avoid misconceptions, ask students
to explain the ways in which the animated charge carriers are
not like actual electrons. For example, current is the measure
of the movement of charge, not of individual electrons—
electrons continue to drift in a random pattern that moves
more in the direction of the current than against it.
Breadboard with a series circuit and multimeter.
rather than focusing on the complex relationship between
total resistance and the individual values. My intention is for
students to realize that the total resistance is less than any of
the individual resistance values.
As students share their data with the class, they quickly
realize that voltage drops are equal in each branch of a
parallel circuit and that the current through each branch
adds up to the total current. I have students discuss why
they initially think that the total resistance is less than the
individual resistors. Students often complain, “But that
doesn’t make sense!” The visualization of electron flow that
the simulations provide aid in this discussion; it allows me
to ask questions about how the simulation shows the charge
flow in each branch.
C o m p l e x c i rc u i t s e x p l o rat o r y
During the third exploratory, students construct a virtual
complex circuit. At this point, they are often proficient with
the PhET program. In this activity, students construct two
complex circuits and then measure voltage and current values. They often look for broad generalizations, so the lab
should include questions that focus on the series and parallel components of the circuit separately.
This lesson requires the most scaffolding on the teacher’s
part. Students want to be “given” the complex circuit rules,
A Virtual Circuits Lab
rather than work through the realization that series circuit
rules are used in some parts of the circuit and parallel circuit
rules are used in others.
C o n ce p t d eve l o p m e n t
After at least three days of building virtual (and possibly
physical) circuits in series, parallel, and complex structures, students are prepared to work on more abstract
problems. At this point, they often want to memorize specific circuit arrangements. I give students a labeled list of
“series” and “parallel” circuit equations each time we do
this activity. Undoubtedly, one student will ask why the
complex circuit equations are not provided. Giving students ample practice, both in groups and as individuals, is
vital to helping them discover how to apply the series and
parallel voltage and current relationships in a non–simple
circuit case. I find it necessary to lead a daily discussion
to remind students that complex circuits do not have one
set of equations. As a class, students fall back on the expectation for a single set of equations for complex circuits
almost every day.
Application lab: Build a complex circuit
Finally, students are assigned a specific total resistance
for which they are to construct their own complex circuit
given certain resistance values. I have created a spreadsheet that generates possible values from the combinations
given. As an extension, students can physically create the
circuit on a breadboard and then check the total resistance
using a multimeter.
The PhET simulations focus students on connecting the
concepts that resistors in series add to the total resistance
and that resistors in parallel generally decrease the total
resistance. The benefit of the physical construction is that
it often serves as a “hook” for students who want to study
electronics further. A formal lab report can be required, but
I like to emphasize the “play” and problem solving inherent
in the activity, so students receive credit when they complete
the task successfully and show me their final product.
Conclusion
The PhET website has many simulations that allow students to create, observe, measure, and analyze—instead
of simply watching an animation over which they have no
control. This learning cycle guides students through experiences that help them develop an understanding of how
current is divided through parallel circuits and how voltage
is divided in series circuits.
The virtual lab allows students to construct circuits that
look like the diagrams found in textbooks and tests; the
physical lab allows students to manipulate real objects and
deconstruct electronic circuits—so they become more than
just “black boxes.” The use of both a virtual lab and a physi-
cal lab provides scaffolding for students, allowing them to
connect the physical and symbolic worlds.
The Atkin and Karplus learning cycle approach (1962)
works well with the virtual labs provided by PhET. The
Circuit Construction Kit makes the exploration less repetitive for students since they can easily construct new circuits.
The application phase allows students to create a circuit using
their own creative thinking.
In my classes, students gave positive feedback about the use
of the simulations and showed much less frustration than previous students who had only worked with breadboards. In this
series of activities, virtual labs can be used to support inquirybased instruction in concert with a physical lab—allowing
teachers and students to reap the benefits of both methods. n
Matthew E. Vick ([email protected]) is an assistant professor in
the Department of Curriculum and Instruction at University of
Wisconsin–Whitewater.
Editor’s note
The full instructions for each of the three exploratory activities
and the application lab are available on The Science Teacher’s website at www.nsta.org/highschool/connections.aspx.
NSTA connections
For more information on circuits, check out the “Electric
and Magnetic Forces: Electrostatics and Current Electricity” NSTA Science Object. NSTA Science Objects are online,
inquiry-based content modules for teachers that are free of
charge. For more information, visit http://learningcenter.nsta.
org/products/science_objects.aspx.
On the web
Physics Education Technology website: http://phet.colorado.edu/
index.php
References
Atkin, J. M., and R. Karplus. 1962. Discovery or invention? The
Science Teacher 29 (5): 45.
Finkelstein, N.D., W.K. Adams, C.J. Keller, P.B. Kohl, K.K.
Perkins, N.S. Podolefsky, S. Reid, and R. LeMaster. 2005.
When learning about the real world is better done virtually: A study of substituting computer simulations for
laboratory equipment. Physical Review Special Topics—
Physics Education Research 1 (1): 010103(1)–010103(8).
Finkelstein N.D., W.K. Adams, C.J. Keller, K.K. Perkins, C.
Wieman, and the Physics Education Technology Project
Team. 2006. High-tech tools for teaching physics: The physics
education technology project. Journal of Online Learning and
Teaching 2 (3): 110–121.
National Research Council (NRC). 1996. National science education standards. Washington, DC: National Academies Press.
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