SOTM LAB: P21
I.
TEACHER NOTES & GUIDELINES
TITLE OF LAB Equipotential and Electric Field Mapping Lab
DEVELOPERS OF LAB
Tom Blon, JD707;James Kirby, JD726; Philip Ousley, JD733; Kirk Reinhardt, JD738;
OVERVIEW OF LAB
DESCRIPTION
In this lab students will consider aspects of the electric field for point charges, parallel
plates, and special configurations, including electric shielding. The students will
consider energy and work aspects of the electric field by constructing and reading maps
of equipotential lines and considering the relationship to them of the electric field lines.
CURRICULUM CONSIDERATIONS
SAFETY CONSIDERATIONS
Keep water away from any electrical equipment. Avoid short circuits. Do not sniff silver
marker. Always unplug the power supply when connecting and disconnecting probes.
Always listen to all teacher safety instructions.
BACKGROUND INFORMATION
A. SCIENTIFIC VIEWPOINT
The direction of the electric field is the direction that a positive charge
would move in that field. Work is only required to move a charge from a
lower potential to a higher potential, the charge has gained potential
energy because work has been done on the charge. There is no difference
of potential between any two points on a given line of potential. The
field lines are normal to the equipotential line and to the surface of the
charged body. The direction is the direction in which a positive test
charge would travel
B. COMMON MISCONCEPTIONS
1) Equipotential lines can cross.
2) Students do not know the relationship between lines of force and
potential lines.
3) Students do not see the similarities and differences between
gravitational, magnetic and electric fields.
4) Connecting two points on a given equipotential with a conductor
will produce a current.(There is no potential difference, V)
5) Work is required to move a charge along line of potential.(W = Vq)
OBJECTIVES
1. Students will be able to map equipotential and field lines.
2. Students will understand energy and work relationships regarding electric fields.
3. Students will be able to define equipotential lines and electric field lines and be able
to explain the difference between them.
EQUIPMENT/MATERIALS
PROVIDED BY SOTM
PASCO 750, laptop, and the Equipotential and field mapper kit (model # PK-9023).
Instruction Manual should be included. A set of meter leads per mapper kit (see page 4
of manual).
Prepared conductor sheets of parallel plates, point charges and matching paper grid
sheets.
Optional: Directions for set up and display of data in a 3 – Dimensional map of
potentials.
Both hard copy directions and disc with following programs attached:
P21pts.xls & p21pll.xls (see attached graphs)
ADVANCE PREPARATION
Clean lab surface area for each lab group expected with electrical outlets for each group.
Teacher should read instruction manual.
Attached will be an Excel procedure for plotting the potential difference to create a 3dimensiuonal map of potential differences for the above listed models. If you choose
this, the students will need to record the potential difference on the attached data sheet.
II. PRE-LAB
PRE-LAB EXERCISE TO ELICIT STUDENTS' PRIOR KNOWLEDGE AND
MISCONCEPTIONS
1. Have students, in groups, come up with real life examples of doing work. Ask students what
they believe doing electrical work means.
2. Ask students what they remember from earth science regarding contour mapping. Hand out
contour maps or use demo chart. Review concept of different altitudes, contour interval and
slope of land.
3. Ask students how they would design a contour map for gravitational potential energy levels
of a 1kg mass about the earth.
4. What is the relationship between the work done on the mass as it travels along a constant
potential energy level at a constant speed?
5. What path is taken by the mass as it increases in potential energy relative to gravitational
lines of force? Decreases?
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DISCUSSION OF PRECONCEPTIONS
1. Each group presents to class their ideas regarding real life examples of doing work. Other
groups will be allowed to comment.
2. Each group presents to the class their contour map design for gravitational potential energy.
Other groups are allowed to comment.
3. Teacher summarizes consensus for #1 and #2 and then asks students to answer #4 and #5
using that information.
4. Teacher tells students that lab activities will help them support or refute their ideas that they
have developed here.
III. EXPLORATION OF SCIENTIFIC PRINCIPLE
& INTRODUCTION OF EXPERIMENTAL
PROTOCOL
PROBLEM
Mapping equipotential lines of oppositely charged geometric shapes (point charges,
parallel plates and special configuration).
EXPERIMENT AND TECHNICAL OPERATION OF EQUIPMENT
1. Describe the apparatus including conductive paper, matching paper grids, probes, 750
interface (which includes the power supply) and laptop computer.
2. Demonstrate, using the parallel plate configuration, different potential “changes” as you
make perpendicular movements of the positive probe and parallel movements of the positive
probe.
IV. ELABORATION OF SCIENTIFIC PRINCIPLE:
INQUIRY-BASED STUDENT INVESTIGATION
PROBLEM
How can the researchers, by using the concept of potential differences, map equipotential lines in
an electric field?
Optional: How can the researcher, by using the concept of potential differences, map lines of
force in an electric field? Potential gradient (E = V/t), compare parallel plates to two point
charges.
HYPOTHESIS OR PREDICTION
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Discuss/sketch with your group members, what would a model of equipotential lines
look like between oppositely charged parallel plates and oppositely charged points?
Optional: Discuss/sketch with your group members, what would a model of lines of
force look like between oppositely charged parallel plates and oppositely charged points?
EXPERIMENTAL DESIGN
1. What are the variables that you will be measuring?
2. What measuring techniques will you use?
3. What tables and graphs will you need to create?
4. List safety precautions that must be observed.
5. Check with your instructor before actually setting up your experiment.
(Suggested voltage is 5 V, which is the maximum output of the 750 interface)
PLAN FOR DATA COLLECTION & ANALYSIS
1. What data are you going to collect?
2. How are you going to organize your data tables, graphs, etc.?
3. Check with your instructor before actually doing your experiment.
CONDUCTING THE EXPERIMENT
Students set up experiments and ask for guidance if necessary.
Checkpoint (Teacher monitors students' investigations in progress.)
ANALYSIS OF DATA
Checkpoint (Teacher checks students' analysis.)
DISCUSSION OF RESULTS
.
COMPARE:
Lab groups compare their maps for the parallel plates, point charges, and the special
configuration.
PERSUADE:
1. Discuss your results with another group and try to reconcile any differences in the
data.
2. Each group should draw conclusions based on the maps generated and explain them
to a neighboring group.
3. Suggest any ideas for future experiments.
RELATE
Can you make a relationship between the electric potential lines of the fields to the
gravitational potential lines in the pre-lab exercise?
Can you predict the direction and relationship of the lines of electric force to the
equipotential lines?
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V.
EVALUATION
POST-LAB SURVEY OF STUDENTS' CONCEPTIONS
Have students retake the pre-lab exercise.
Compare pre-lab and post-lab responses.
TRADITIONAL
Select five to ten NYS Regents type questions.
ALTERNATIVE
Give the students a piece of graph with a varied electric field and have them draw the
equipotential lines. (Time permitting, teacher could demonstrate on the mapper kit)
1) positive point charge & negative plate
2) two positive points charges
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Appendix for using Excel spreadsheet:
Plan “a”, no attached disc.
A) Creating data table
1) On the second computer load excel.
2) Leave cell A1 empty.
3) Starting in A2 and ending in A16, enter numbers 0 through 28 by 2s.
4) Starting is B1and ending in L1, enter numbers 0 through 20 by 2s.
5) These will correspond to the needed cross hairs on the conductive paper for
gathering potentials.
6) The students will enter in data to corresponding cells as another student reads the
potential differences from the interface equipment from each point.
B) Mapping data into a 3 – dimensional graph.
1) Highlight cells A1 through L16.
2) Click on the bar graph icon.
3) Choose chart type “surface”
4) Choose chart sub type “3-D surface” (top left).
5) Click next
6) Click next
7) Click next
8) Click potential
9) Right click on legend
10) Left click format legend
11) Click scale
12) Change major unit to 0.3
13) Click OK
14) Click and drag the graph to the right of the data.
15) You can rotate the 3-D image by clicking on one of the corners of the graph and
rotating the mouse.
C) Printing your map.
1) Click on File
2) Click page set up.
3) Choose landscape.
4) Click Print
Plan “b”, disc attached.
A)
1)
2)
3)
B)
1)
2)
3)
4)
Opening excel programs
On the second computer load excel.
Open “P21pts.xls or P21pll.xls” (pts is for points & pll is for parallel plates)
The students will enter in data to corresponding cells as another student reads the
potential differences from the interface equipment from each point.
Printing your map.
Click on File
Click page set up.
Choose landscape.
Click Print
This material is based upon work supported by the National Science Foundation under Grant No. ESI 9618936. Any opinions,
findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the
views of the National Science Foundation.
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