Resistance Lesson Plan – John Nice
South Gwinnett High School
Problem:
The concept of resistance is a property that depends on the geometric properties of length and cross
section and a material property known as resistivity. Resistivity is a function of the material the resistor
is made of and the temperature of the material.
The student will determine the resistance of a material as a factor of length, cross sectional area and
material.
Abstract:
Ohm’s Law and the concepts of current, voltage and resistance are crucial to a basic understanding of
electricity. The lesson has students doing two lab exercises, the first a guided lab, which if done
correctly provides data with a high correlation, while the second is open inquiry and allows the student
to develop their own methods and test their own variable. This should lead to a deeper level of concept
knowledge and inderstanding.
Alignment with Standards:
Gwinnett County Academic Knowledge and Skills
21) calculate the values of current, voltage, resistance and power in various circuits using Ohm's Law
(GPS)
21a) relate electric power to current and voltage
21b) compare and contrast series and parallel circuits
21c) construct and analyze simple series and parallel DC circuits in the laboratory
21c1) demonstrate proper use of ammeters and voltmeters in measuring voltage and current and
resistance through the use of Ohm’s Law
21d) illustrate and analyze through the use of Ohm’s Law steady-state DC circuits in series and parallel
to determine the voltage across, current through, total resistance of and power dissipated/added by
each element in the circuit (GPS)
Georgia Performance Standards
SP5. Students will evaluate relationships between electrical and magnetic forces.
a. Describe the transformation of mechanical energy into electrical energy and the
transmission of electrical energy.
b. Determine the relationship among potential difference, current, and resistance in a direct
current circuit.
c. Determine equivalent resistances in series and parallel circuits
SCSh3. Students will identify and investigate problems scientifically.
a. Suggest reasonable hypotheses for identified problems.
b. Develop procedures for solving scientific problems.
c. Collect, organize and record appropriate data.
d. Graphically compare and analyze data points and/or summary statistics.
e. Develop reasonable conclusions based on data collected.
f. Evaluate whether conclusions are reasonable by reviewing the process and checking
against other available information.
SCSh4. Students will use tools and instruments for observing, measuring, and manipulating
scientific equipment and materials.
a. Develop and use systematic procedures for recording and organizing information.
b. Use technology to produce tables and graphs.
c. Use technology to develop, test, and revise experimental or mathematical models.
SCSh5. Students will demonstrate the computation and estimation skills necessary for
analyzing data and developing reasonable scientific explanations.
a. Trace the source on any large disparity between estimated and calculated answers to
problems.
b. Consider possible effects of measurement errors on calculations.
c. Recognize the relationship between accuracy and precision.
d. Express appropriate numbers of significant figures for calculated data, using scientific
notation where appropriate.
e. Solve scientific problems by substituting quantitative values, using dimensional
analysis and/or simple algebraic formulas as appropriate.
SCSh6. Students will communicate scientific investigations and information clearly.
a. Write clear, coherent laboratory reports related to scientific investigations.
b. Write clear, coherent accounts of current scientific issues, including possible
alternative interpretations of the data
c. Use data as evidence to support scientific arguments and claims in written or oral
presentations.
d. Participate in group discussions of scientific investigation and current scientific
issues.
AP Physics Standards
Essential Knowledge 1.E.2: Matter has a property called resistivity
a. The resistivity of a material depends on its molecular and atomic structure.
b. The resistivity depends on the temperature of the material.
Learning Objective 1.E.2.1:
The student is able to choose and justify the selection of data needed to determine resistivity
for a given material.
Science Practice 4: The student can plan and implement data collection strategies in relation to a
particular scientific question.
Objectives:
The student will be able to explain how length of a wire affects the resistance and provide evidence for
their explanation.
The student will be able to explain how the cross sectional area affects the resistance of a resistor and
provide evidence for their explanation.
The student will be able to explain how the composition of the material can affect the resistance of a
resistor and provide evidence for their explanation.
Anticipated Learner Outcomes:
The learner will be able to determine the resistance of an object given its length, cross sectional area
and resistivity, or given the resistance, solve for any one of the three factors that determine the
resistance.
The learner will be able to conduct an experiment to determine the resistance of an object using
multimeters and a power supply. The learner can also determine either length, cross sectional area or
resistivity by measuring the other two variables.
The learner will be able to solve problems involving Ohm’s Law and Resistivity.
Assessment/Rubric:
RUBRIC FOR ASSESSING LAB REPORTS
NOTE: it is assumed that all lab reports will be written on a computer
1
2
3
4
Beginning or incomplete
Developing
Accomplished
Exemplary
Abstract/Summary
Several major aspects of the Abstract misses one or more Abstract references most of the
experiment are missing, student major aspects of carrying out the major aspects of the experiment,
displays a lack of understanding experiment or the results
some minor details are missing
about how to write an abstact
Abstract contains reference to all
major aspects of carrying out the
experiment and the results, wellwritten
Introduction
Very little background
information provided or
information is incorrect
Some introductory information,
but still missing some major
points
Introduction complete and wellwritten; provides all necessary
background principles for the
experiment
Experimental
procedure
Missing several important
experimental details or not
written in paragraph format
Written in paragraph format, still Written in paragraph format,
missing some important
important experimental details
experimental details
are covered, some minor details
missing
Well-written in paragraph
format, all experimental details
are covered
Spelling, grammar,
sentence structure
Frequent grammar and/or
spelling errors, writing style is
rough and immature
Occasional grammar/spelling
Less than 3 grammar/spelling
errors, generally readable with
errors, mature, readable style
some rough spots in writing style
All grammar/spelling correct and
very well-written
Appearance and
formatting
Sections out of order, too much
handwritten copy, sloppy
formatting
Sections in order, contains the
minimum allowable amount of
handwritten copy, formatting is
rough but readable
All sections in order, wellformatted, very readable
Introduction is nearly complete,
missing some minor points
All sections in order, formatting
generally good but could still be
improved
Score
3
6
9
12
Beginning or incomplete
Developing
Accomplished
Exemplary
Figures, graphs, tables contain
errors or are poorly constructed,
have missing titles, captions or
numbers, units missing or
incorrect, etc.
2 components: graphs, tables or
questions are incomplete or one
is missing.
One component: graphs, tables,
questions is incomplete
Data is complete and relevant.
Graphs are labeled and titled and
show trends. Tables are easy to
read and units are provided. All
questions are answered
completely and correctly
Discussion
Very incomplete or incorrect
interpretation of trends and
comparison of data indicating a
lack of understanding of results
Some of the results have been
correctly interpreted and
discussed; partial but incomplete
understanding of results is still
evident
Almost all of the results have
been correctly interpreted and
discussed, only minor
improvements are needed
All important trends and data
comparisons have been
interpreted correctly and
discussed, good understanding
of results is conveyed
Conclusions
Conclusions missing or missing
the important points
2 Components missing:
Summary, Data, Hypothesis,
Errors
One component of conclusion is
missing: Summary, Data,
Hypothesis, Errors
Conclusion summarizes
experiment, cites data,
addresses hypothesis and cites
sources of error.
Results:
data, figures,
graphs, tables, etc.
Total Score
Background:
Ohm’s Law describes the relationship between current, electric potential difference (voltage) and
resistance. Resistance can be defined as the ratio of the voltage to the current. Commonly, Ohm’s Law
is written as V=IR, where resistance is a constant in the problem. Many materials follow Ohm’s Law and
give a linear relationship between current and voltage. Some materials do not follow Ohm’s Law. An
example of this is an incandescent light bulb. The current is not linear with the voltage, as the resistance
changes due to heating of the filament.
Generally, the property of resistance depends on the length, cross sectional area, the temperature and
the material a resistor is made of. The resistivity of a resistor is a value which describes the material and
temperature of the resistor.
Resistance (R) can be calculated by the following equation:
R = ρL/A
ρ is the resistivity of the resistor. This can be calculated by the following equation
ρ=ρo[1+α(T-To)] where ρo is the resistivity at a reference temperature(To), usually 20⁰C (room
temperature), and α is the temperature coefficient of resistivity. α is an empirical value and if the
temperature change is large, α cannot be assumed to remain the same.
Materials and Supplies:
Guided Lab for Ohm’s Law: Pasco Spark, Current Voltage Sensor, 3 resistors between 10 and 25 ohms.,
6V lightbulb
Inquiry Lab for Resistivity: Nichrome Wire: 16,18 and 22 gauge, Pencils of varying hardness, 2
Multimeters with leads or alligator clips, Meterstick and ruler, Power Supply
Plan:
Day 1: Introduce the concept of current and resistance with a Powerpoint presentation. Assign the
prelab for Ohm’s Law Lab
Day 2: Lab 1 – Ohm’s Law – Students collect data for current and voltage for 3 resistors between 10 and
25 ohms and a light bulb. See attached lab.
Day 3: Graphing of data. Students hand graph each of the 3 data sets and calculate the resistance of
the resistor. If the data is more than 10% off of the assigned value, the student group needs to repeat
that measurement and graph the new data.
Day 4: Ohm’s Law Practice Problems, Assign Prelab for Resistivity Lab
Day 5: Resistivity Lab – See Attached Lab
Day 6: Resistivity Lab
Day 7: Post lab Discussion
Day 8: Resistivity Practice Problems
Summary:
The student enters the unit with a basic concept of electrical force, and then develops an understanding
of the concept of resistance. The first lab is designed to reinforce the student’s graphing skills, by
making the student determine what the slope is and what the meaning of the slope is. The concept of
Ohm’s Law is reinforced with a problem set. The second lab allows the students to conduct a lab with
very little guidance, and has the groups report their results to each other and discuss the meaning. Each
group may approach the lab in different ways and get different results. The variables affecting
resistance are reviewed with the following problems set. This gives the student a chance to learn about
the variables affecting resistance even if their group did not determine a particular variable.
Finally, the students will learn about concepts that do not follow the rules: Graphene, which is a ballistic
conductor and superconductors.
Ohm’s Law Lab
Purpose: Determine the validity of Ohm’s Law applied to various resistive objects.
Safety:
1. Resistors get hot! Turn on the power supply, measure, turn off.
2. Voltages must be measured in parallel. Make sure you understand how this is done before you
turn on the power supply.
3. Currents are measured in series. Make sure you understand how this is done before you turn on
the power supply.
4. Do not allow the alligator clips to touch the power supply. They can short circuit to the
power supply case.
The light bulbs are rated for 6.2V. If you burn out a light bulb, you will lose points on the
lab.
Procedure: 1. For each resistor, find the voltage across it and the current through it. Do this for
voltages between 2.5 to 8V increasing ½ volt each measurement. Do not go to
8 V. Record this in a data table for each resistor.
2. Graph the current vs. the voltage. Determine the slope of each graph? What is the meaning of the
slope of the graph?
3. Determine the resistance of the resistor. Find the relative error from the rated value of the resistor.
If your error is greater than 10%, than repeat the measurements for that resistor. You do not have a
rated value for the light bulb, so do not do that one over.
4. Turn in to me a data table and graph for each resistor. Turn in the calculations and results for steps
2 and 3.
5. Observe the increase and decrease of voltage on a light bulb. Sketch the graph of the Current vs.
Voltage for the light bulb.
6. Answer the following:
In your own words, draw the method for measuring voltage.
In your own words, draw the method for measuring current.
Compare the graphs you made for each resistor with the sketch of the graph of the light bulb. Is the
light bulb ohmic?
Resistance
Voltage (V)
Resistance
Current (A)
Light Bulb Sketch
Voltage (V)
Resistance
Current(A)
Voltage (V)
Current (A)
What Factors Affect Resistance?
Purpose: Your goal is to determine the resistance of various materials using the techniques used in the
Ohm’s Law Lab. The materials given to you vary in their composition. Determine how these variances
affect the resistance. Brainstorm what other factors you might be able to change.
Materials Provided:
3 wires made of Nichrome. Each wire has a different thickness: 22 gauge, 18 gauge and 16 gauge.
Pencils with the ‘lead’ exposed at each end. Each pencil is a different type of hardness. This means the
percentage of graphite and clay vary. The diameter of each pencil can also very. Look at the provided
chart to get the diameters.
2 multimeters
Ruler
Meterstick
Prelab:
1. Define resistance
2. Draw a schematic diagram of the setup you will use to determine the resistance.
3. Look up what a rheostat is.
Procedure:
In discussion with your lab group, decide on a procedure you will use to determine the resistance of a
sample and what variables you are able to vary. Remember to vary only one variable at a time if
possible. Write down the procedure you use in your lab notebooks.
Analysis:
What properties did you test in your experiment?
How did changing a property of a material affect the material’s resistance? Provide evidence of your
answer.