Creating a Wheatstone Bridge
Subject Area(s)
Physical Science, Engineering
Associated Unit
Physics/Circuits
Lesson Title
Building a Macro MEMS
MEMS
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Grade Level 8-9
Lesson # 1 of 2
Time Required 2-3 blocks
Summary
The first day of the lesson will begin with a PowerPoint review of circuits and their components how they
are created and measured and the different types. Students will complete guided notes from the
PowerPoint. Students will display their mastery of the circuits content by content creating a mini-individual
science interactive notebook on circuits and by manipulating wires, resistors and light bulbs to create
different circuits. The notebook will include detailed diagrams of the different type of circuits. The teacher
will then distribute index cards to each group that has specific prefixes that mean small things such as
Macro, Micro, Nano, Giga, Tera, Mega. Students will be allowed to use their cell phones to look up the
prefixes and associate the prefix with a device. Students will create a poster of the important devices
associated with their prefix. This day will end with an assessment covering circuits. On the second day
of the lesson, the teacher will introduce Enabling Nanotechnology PowerPoint with students. With the
new vocabulary introduced to students in the PowerPoint, they will create Frayer model word maps with
words such as nanotechnology, nanofabrication, Ohms Law and pressure sensor. Students will then be
introduced to the “Engineering Design Process” with a diagram and asked to compare and contrast this
process to the Scientific Method using a Venn diagram. This class period will end with a reading on Sir
Charles Wheatstone and the Wheatstone Bridge which will prepare students for the culminating lab on
day three. The culminating activity of the lesson will be creating a Wheatstone Bridge on day three.
Students will be provided with the necessary materials and procedures to create and measure the
resistance of their very own Wheatstone Bridge.
Engineering Connection
Nanotechnology and pressor sensor fabrication are the new waves of tecchnology. Through this lesson
students will have a better understanding of the imporatance of engineering, the engineering process and
how engineering is involved in just about every aspect of technology. The culminating activty will allow
students to experience the process that engineers encounter when develping new devices.
Engineering Category
1. Relating science and/or math concept(s) to engineering
2. Engineering analysis or partial design
3. Engineering design process
Keywords
MEMS, Nanotechnology, Nanofabrication, Conductor, Wheatstone bridge, Resistance, Resistivity, Ohms
Law, Pressure sensor, Circuit
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Educational Standards (List 2-4)
ITEA
Standard 8. Students will develop an understanding of the attributes of design.

E. (6-8) Design is a creative planning process that leads to useful products and systems.

F. (6-8) There is no perfect design.

G. (6-8) Requirements for design are made up of criteria and constraints.

H. (9) The design process includes defining a problem, brainstorming, researching and
generating ideas, identifying criteria and specifying constraints, exploring possibilities, selecting
an approach, developing a design proposal, making a model or prototype, testing and evaluating
the design using specifications, refining the design, creating or making it, and communicating
processes and results.
NGSS
MS-ETS1-4.
Develop a model to generate data for iterative testing and modification of a proposed
object, tool, or process such that an optimal design can be achieved.

ETS.1.C –The iterative process of testing the most promising solutions and modifying what is
proposed on the basis of the test results leads to greater refinement and ultimately to an optimal
solution
LAFS.8.W.1.1
Write arguments to support claims with clear reasons and relevant evidence.
a. Introduce claim(s), acknowledge and distinguish the claim(s) from alternate or opposing
organize the reasons and evidence logically.
claims, and
b. Support claim(s) with logical reasoning and relevant evidence, using accurate, credible sources and
demonstrating an understanding of the topic or text.
c. Use words, phrases, and clauses to create cohesion and clarify the relationships among claim(s),
counterclaims, reasons, and evidence.
d. Establish and maintain a formal style.
e. Provide a concluding statement or section that follows from and supports the argument presented
MAFS.912.A-CED.1.4
Rearrange formulas to highlight a quantity of interest, using the same reasoning as in solving equations.
For example, rearrange Ohm’s law V = IR to highlight resistance R.
NGSSS
SC.8.N.1.6
Understand that scientific investigations involve the collection of relevant empirical evidence, the use of
logical reasoning, and the application of imagination in devising hypotheses, predictions, explanations
and models to make sense of the collected evidence.
Pre-Requisite Knowledge
Students will have prior knowledge of electricity and circuits.
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Learning Objectives
After this lesson, students should be able to:
 Calculate differences in resistance across a pathway
 Apply Ohm’s Law V=IR
 Effectively communicate the difference between different circuits

Explain what Nanotechnology is and its importance

Compare and Contrast Engineering Design Process and Scientific Method
Introduction / Motivation
The teacher will begin the lesson by displaying different pictures from the summer RET experience and
asking probing questions. The students will see a picture of teachers in the clean room performing
various steps in the fabrication process as well as a picture of the Wheatstone Bridge.
Sample Probing Questions

What do you think is going on?

Why are the teachers dressed like that?

What do you see?

How might what you see involve circuits?
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Lesson Background & Concepts for Teachers
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Ohm's law describes the way current flows through a resistance when a different electric potential
(voltage) is applied at each end of the resistance. One way to think of this is as water flowing through a
pipe. The voltage is the water pressure, the current is the amount of water flowing through the pipe, and
the resistance is the size of the pipe. More water will flow through the pipe (current) the more pressure is
applied (voltage) and the bigger the pipe is (lower the resistance).
Example Problems
1. If the resistance of an electrical circuit is increased, what will happen to the current assuming the
voltage remains the same?
Answer: The current will decrease.
2. If the voltage across a resistance is doubled, what will happen to the current?
Answer: The current will double as well.
Explanation: If you look at the equation V= IR, if R stays the same then if you multiple V*2 (double the
voltage), you must also double the current for the equation to remain true.
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Vocabulary / Definitions
Word
MEMS
Nanotechnology
Nanofabrication
Wheatstone Bridge
Circuit
Ohm’s Law
Resistance
Resistivity
Conductor
Ammeter
Ampere
Pressure Sensor
Transducer
Definition
Micro-Electro-Mechanical-Systems (MEMS) is the integration of mechanical
elements, sensors, actuators, and electronics on a common silicon substrate
through microfabrication technology.
The study and application of things that are one billion times smaller than a
meter that are used across all science fields, such as chemistry, biology,
physics, materials science, and engineering.
The design and manufacture of devices with dimensions measured in
nanometers. One nanometer is 10-9 meter, or a millionth of a millimeter.
A four armed bridge circuit, each arm having a resistor. It is used to
measure an unknown resistance by balancing two arms of the bridge, one of
which contains the unknown resistance.
A complete and closed path around which a circulating electric current can
flow.
The law stating that the direct current flowing in a conductor is directly
proportional to the potential difference between its ends. It is usually
formulated as V=IR, where V is the potential difference, or voltage, I is the
current, and R is the resistance of the conductor.
A measurement of the difficulty encountered by a power source in forcing
electric current through an electrical circuit, and hence the amount of power
dissipated in the circuit and is measured in ohms.
The measurement of how strongly an electric current resist to flow
An object or type of material that permits the flow of electric charges in one
or more directions.
A measuring instrument used to measure the electric current in a circuit.
The unit of measurement used to measure an electric current
Acts as a transducer; it generates a signal as a function of the pressure
imposed
A device that converts one form of energy to another form
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Associated Activities
Day 1
Step 1- PowerPoint review of circuits and their components how they are created and measured and the
different types. Students will complete guided notes from the PowerPoint. Students will display their
mastery of the circuits content by content creating a mini-individual science interactive notebook on
circuits and by manipulating wires, resistors and light bulbs to create different circuits. The notebook will
include detailed diagrams of the different type of circuits.
Step 2-The teacher will then distribute index cards to each group that has specific prefixes that mean
small things such as Macro, Micro, Nano, Giga, Tera, Mega. Students will be allowed to use their cell
phones to look up the prefixes and associate the prefix with a device. Students will create a poster of the
important devices associated with their prefix.
Step 3-This day will end with an assessment covering circuits.
Day 2
Step 1-The teacher will introduce Enabling Nanotechnology PowerPoint with students. With the new
vocabulary introduced to students in the PowerPoint.
Step 2 – Students will create Frayer model word maps with words such as nanotechnology,
nanofabrication, Ohms Law and pressure sensor.
Step 3 - Students will then be introduced to the “Engineering Design Process” with a diagram and asked
to compare and contrast this process to the Scientific Method using a Venn diagram.
Step 4 – Students will read and answer questions on Sir Charles Wheatstone and the Wheatstone Bridge
which will prepare students for the culminating lab on day three.
Day 3
Step 1 - Students will be provided with the necessary materials and procedures to create and measure
the resistance of their very own Wheatstone Bridge.
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Wheatstone Bridge Lab (procedure adapted from Nezih Pala)
Supplies provided by Instructor
meter with clip-on leads
Supplies included in AMERI Kit
plastic cups (empty and unused)
– 2 packs 15 leads each (shown)
– conductive on both sides (3M) (shown)
(2) leads with alligator clip at each end (Leads should be the same length)
-25ml
rning Module - Instructor Guide
- Participant Guide
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Procedures
Creating Bridge Pattern
1. Using the stencil provided cut the bridge pattern from a piece of the cardboard or cardstock.
2. Cut the neck off the balloon to about 4 cm from top opening or at least 1 cm below the curvature of
neck
3. Stretch the balloon tightly over the open end of the paint can. You want an “even” stretch.
4.Secure the edges of the balloon to the can with painter’s tape.
Creating the leads and bridge pattern
1. Center the template over the balloon diaphragm as shown in
2. Outline the pattern with a marker onto the top of the diaphragm. Remove template from diaphragm.
3. Cut four – 8 – 10 cm strips of conductive copper tape.
4. Remove the backing off one strip of conductive tape. Place one end of the tape on the
membrane (balloon) in line and on top of part of the “circuit”
5. Pinch the middle of the strip of tape to create a tab and attach the other end of the
conductive tape to the side of cup. The tab will be used to connect the meter leads for measuring
resistance and voltage.
6. Repeat steps 5 and 6 with the other three leads (strips of conductive tape).
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Making the Conductive Material (carbon paste)
1. Put on gloves and safety glasses.
2. Carefully break one pack of the graphite leads (15 pieces) into small pieces and place in the
mortar.21
3. Grind the graphite into as fine of a carbon powder as possible. Grind until you see no “grain
pieces” and the graphite is a powder. The finer the better. You will be mixing this powder with
rubber cement and then forcing the mixture through a syringe tip. A small graphite chunk could
clog the syringe.
4. Pour the carbon powder onto sheet of paper or into the coffee filter. Use a small brush to get
all of the carbon out of the mortar.
5. Fold the paper/filter and carefully pour all of the powder into a glass vial.
6. Using the syringe with tip attached, extract approximately 3 ml of rubber cement.
7. Transfer the rubber cement to the vial containing the graphite powder.
8. Unfold a large paperclip, but leave the smaller looped end intact.
9. Using the paperclip, stir the powder and rubber cement mixture in the vial. The color of the
mixture should be black, and the viscosity (thickness) should be close to the original cement. If
it is too thick, add a little more rubber cement. If too thin, add more carbon powder. (A
comment – You will be applying this graphite/rubber cement mixture onto the diaphragm in
the same manner as decorating a cake; therefore, the viscosity of the mixture should similar to
that of toothpaste.)
Your conductive material is now made and ready for use.
Making a Conductive Bridge
1. Pull liquid from the vial with the syringe. Fill the syringe with the mixture.
2. To eliminate the air from the syringe, insert the paperclip into the tip of the needle, through
the liquid and into the air gap at the top of the syringe.
3. Burp the air from the syringe, by gently compressing the liquid in the syringe until a little
comes out of the needle. *Note: It is important when filling the syringe that there are no air
bubbles because when applying the conductive material it is essential that there are no gaps in the lines.
4. If the syringe does not have at least 2 ml of liquid, place the syringe tip back into the vial and
continue to fill the syringe to the 2 ml mark.
5. Using a wipe or paper towel, wipe the tip clean.
6. Using the syringe, carefully apply about a 1 to 2 mm line (width) of your conductive material
(rubber cement and graphite mixture) following the pattern transferred from the template. Try
to keep the width and height of the carbon/cement line consistent. Be sure to flow ON TOP of
and over the copper wire at the bridge corners. You need to make good electrical contact.
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7. Check for any “opens” in your circuit. Close them with the graphene solution.
8. Before testing your bridge circuit, you should let it set for 15 to 30 minutes.
9. Squeeze any unused graphite/cement mixture from the syringe, back into the vial.
10. Cap the vial. The remaining mixture should stay fluid for several weeks.
11. Clean or properly dispose of the syringe.
Working the Circuits
1. Clip one of the leads from the multimeter to one of the connecting leads (copper tabs).
2. Clip the other multimeter lead to the "opposite" connecting lead as shown below in.
(Do not hook the battery up yet, you will only be measuring resistance of the circuit.)
3. Gently press down a couple of times on the diaphragm to pre-stretch it.
4. Set your multimeter to read resistance.
5. Record your reference circuit's total resistance. RR = _________________
(NOTE: The multimeter may indicate a continual drop in pressure as the diaphragm comes to
rest at its reference position.)
6. Gently push down on middle of the balloon. You should see the resistance change.
NOTE: Be creative. Develop a systematic approach to “applying pressure”. For example, you
could use coins, small weights, marbles, or any of the same object that is heavy enough to “flex”
the diaphragm. Of course if the object is conductive (e.g., coins), a balloon should be used as an
insulator between the weights and the circuit.
7. Record the resistance for three different applied pressures, increasing the pressure before
each recording.
a. R1 = __________________
b. R2 = __________________
c. R3 = __________________
(NOTE: Because of the elasticity characteristics of the balloon, your resistance reading ay not
return to the original reference resistance once the applied pressure is removed. The balloon
may lose some of its original rigidity as different pressures are applied.)
8. How did the applied pressure affect the resistance of the bridge?
9. Explain how the following formula relates to your Wheatstone bridge circuit. = ( / )
10. Draw the equivalent circuit with the resistance meter hookup in the space below.
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Voltage
12. Switch meter to measure voltage.
13. Record initial voltage. VR = _______________________
NOTE: A balanced bridge should have a zero voltage as VR. Why does your bridge not measure
zero?
14. Press down on the middle of the diaphragm.
15. Record the voltage for three different pressures, increasing the pressure before each recording.
a. V1 = __________________
b. V2 = __________________
c. V3 = __________________
16. How did the applied pressure affect the voltage across the bridge?
The following steps allows you to further explore this device and the effects that pressure has
on the resistance and voltage of a Wheatstone bridge sensing circuit.
17. Using the ice pick or nail, punch a hole in the side of the paint can. The hole should be big
enough to insert the TT tip of a syringe.
18. Pull an empty syringe to about 1.5 ml of air.
19. Place the tip of the syringe in the hole. Make it snug and as airtight as possible.
20. You can now simulate increases in pressure (pushing on the syringe) and decreases in
pressure (pulling on the syringe).
21. Test your pressure sensor model using various changes in pressure.
22. This model could also be used to show how a MEMS pressure sensor is affected by
temperature. Find ways to increase or decrease the ambient temperature or the temperature
of the air trapped inside the can. Study the effects on the circuit’s output.
Post Lab Questions
1. In the above procedure, what factors could have an effect on the outcome (the resistivity of
the bridge circuit)?
2. What is meant by the “reference” voltage or reference resistance of the Wheatstone bridge?
Does this stay consistent? Why or why not?
3. What determines the reference voltage / resistance?
4. What causes a change in resistance or voltage?
5. Describe three (3) MEMS that use a diaphragm pressure sensor.
6. How could this pressure sensor model be improved upon?
Lesson Closure
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This lesson has taught how the macro world and the micro world are compared with respect to the
behavior of electrical flow. There is a direct relationship between the two. The scale may change but the
underlying concepts remain the same. As a society there has been a paradigm shift from a large macro
scale world to one of microscopic proportions. The quest for miniaturization has led us into the realm of
Nanotechnology. This lesson allows students to observe firsthand how more can be accomplished, with
less space using newly developed technology. The future of the scientific community relies on the
continuation of our experimentation. The big questions to consider are how this newly developing
technology will continue to advance, and how it will ultimately impact our everyday lives.
Assessment
Pre-Lesson Assessment
Supply a picture of MEM’s, teachers in cleanroom
Students will answer probing questions in the Science Interactive Notebooks

What do you think is going on?

Why are the teachers dressed like that?

What do you see?

How might what you see involve circuits?
Post-Introduction Assessment

Exit Slip on circuits
Lesson Summary Assessment
Students will write at least a report that explains, the importance of a Wheatstone Bridge in a circuit,
Nanotechnology how this newly developing technology will continue to advance, and how it will ultimately
impact our everyday lives. The report must be between 3-5 pages long and include the experiences from
the lesson.
Homework
Research and investigate what devices MEMS are included in. Discern what potential industries are
poised for growth based on this budding multi-billion dollar industry. Create a power point or other
graphic presentation to introduce your class mates to your findings.
Lesson Extension Activities
FIU Engineering Expo Field Trip
Additional Multimedia Support
See Attached Power Point constructed by the researchers/authors of this lesson.
Attachments



Frayer model template
Scientific Method vs. Engineering Process Diagram
Enabling Nanotechnology Powerpoint
Contributors
Kent Landon
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Ebonie Battle
Henry Arendse
Supporting Program
FIU RET
http://www.cec.fiu.edu/tag/nanotechnology/
www.dadeschools.net<http://www.Dadeschools.net>
Classroom Testing Information
Summative Testing will be based on the selected parts of this lesson. Each instructor may select different
sections of this plan to use; therefore, each instructor’s assessment will vary.
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