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IIT/FIELD MUSEUM – High School Transformation Project
Lesson: Ohm, Ohm on the Range
Prentice Hall Conceptual Physics
Unit V Electricity and Magnetism
Chapter 35 Electric Circuits
Section 35.3 Series Circuits
Section 35.4 Parallel Circuits
Guiding Questions:
1. What is the relationship between the current and the voltage across the
resistances in a series circuit.
2. What is the relationship between the current and the voltage across the
resistances in a parallel circuit.
Context of Lesson
Students will investigate the relationship between currents, voltages, and resistances
in series and parallel circuits, but the students must have prior knowledge so that they can
make the circuits. Students need to know what voltage, current, and resistance is.
Students need to be able to use Ohm’s Law to calculate resistance from what they
measure. And, students need to know how to build circuits with resistors in series and
parallel and how to measure voltage across these resistors and the current flowing
through them.
Main Goals/Objectives
As a result of this activity, students will be able to:
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build series and parallel circuits
measure the voltage across and current though items in series and parallel
circuits
calculate the individual resistance and equivalent resistance of items in series
and parallel circuits
identify relationships among voltages, currents, and resistances in both series
and parallel circuits
Nature of Science: Integrated Theme
 Explain that scientific knowledge is tentative due to new evidence or new
interpretation.
 Explain that scientists’ creativity influence their doing inquiry so they may have
different observations and interpretations of the same phenomena.
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Distinguish observations from inferences, explain that inferences should be based
on observations, and explain that the development of scientific knowledge
involves both observations and inferences so scientific knowledge is partially
inferential.
Explain that scientists’ background knowledge influence their doing inquiry so
they may have different observations and interpretations of the same phenomena.
Explain how scientific theories are different from scientific laws: Scientific laws
are more likely observable patterns and scientific theories are explanations for
observable patterns.
Explain that scientific knowledge should be based on empirical data.
Scientific Inquiry: Integrated Theme
 Explain that scientific investigations all begin with a question, but do not
necessarily test a hypothesis
 Explain that there is no single scientific method and provide at least two different
methods
 Explain that inquiry procedures are guided by the question asked
 Explain that all scientists performing the same procedures may not get the same
results
 Explain that inquiry procedures can influence the results
 Explain that research conclusions must be consistent with the data collected
 Explain that scientific data are not the same as scientific evidence
 Explain that explanations are developed from a combination of collected data and
what is already known
General Alignment to Standards
STATE GOAL 11: Understand the processes of scientific inquiry and
technological design to investigate questions, conduct experiments, and solve
problems
A. Know and apply the concepts, principles and processes of scientific inquiry.
 ILS 11.A.4a Formulate hypothesis referencing prior research and
knowledge
 ILS 11.A.4b Conduct controlled experiments or simulations to test
hypotheses
 ILS 11.A.4c Collect, organize and analyze data accurately and precisely
STATE GOAL 12: Understand the fundamental concepts, principles and
interconnections of the life, physical and earth/space sciences.
C. Know and apply concepts that describe force and motion and the principles
that explain them.
 ILS 12.C.2a Describe and compare types of energy including light, heat,
sound, electrical and mechanical.
D. Know and apply concepts that describe force and motion and the principles
that explain them.
ILS 12.D.3a Explain and demonstrate how forces affect motion (e.g.,
action/reaction, equilibrium conditions, free-falling objects).
PSAE Goals:
STANDARD 12D – FORCE AND MOTION
12.11.80 Understand that the electrical force is a universal force that exists
between any two charged objects. Opposite charges attract, like charges repel.
The strength of the force is proportional to the charges, and, like gravity, it is
inversely proportional to the square of the distance between the charged bodies.
12.11.81 Understand that between any two charged particles, the electrical force
is vastly greater than the gravitational force. Most observable forces such as those
exerted by a coiled spring or friction may be traced to electrical forces acting
between atoms and molecules.
Materials – for each lab group
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DC Voltage Source – variable AC to DC supply preferred so that
students can adjust the voltage – a 6V lantern battery may be used
4 Digital Multi-Meters (DMM) – to measure voltage or current
5 resistors: 3 of equal resistance (10Ω works well) and two of different
resistances (5Ω and 25Ω for example) – ceramic resistors are preferred
unless students have learned how to read banded resistors
Wires: a selection of wires with one alligator clip and one banana plug
and two banana plugs. For the most complicated circuit (three resistors
in parallel) each group will need a minimum of 6 wires with one
alligator and one banana and 4 wires with two banana plugs. Double
alligator clips may be used; more often in Part 1.
Two Voltage Probes – these wires are often included with DMM’s.
Each group only needs two and more then that usually leads to
confusion as they help students remember to measure voltage in
parallel by touching the probes to the resistor.
Lesson
The lab activity can be done in two days. On day one, the students will do Part 1 (series
circuits). On day two, the students will do Part 2 (parallel circuits). To save time, the
students can do the calculations and analysis questions for homework. Use the third day
to discuss the lab findings during the two parts of the lab.
Day 1: Part 1: Series Circuits
Bell Ringer
Ask the students what is the difference between a “closed” and “open” circuit.
Lab Activity
Allow students to work in their lab groups to build the directed circuits and take
measurements. Students should read the directions very carefully. Sometimes they are
asked to make a prediction before taking measurements. If groups are running low on
time, advise them to build the circuit, take measurements and avoid the calculations and
analysis questions for the time being.
Students will build a circuit that gets progressively more complicated. The circuit
begins with one resistor (highest resistance resistor), and then another resistor of different
resistance will be added in series. Finally, a third resistor of different resistance will be
added in series. For each circuit, students will measure current, voltage, calculate
resistance using Ohm’s Law, and calculate the equivalent (total) resistance in the circuit.
Homework
Complete all calculations and answer the analysis questions for Part 1.
Day 2: Part 2: Parallel Circuits
Bell Ringer
Ask the students to explain the difference between a parallel circuit and a series circuit.
Lab Activity
Allow students to work in their lab groups to build the directed circuits and take
measurements. Students should read the directions very carefully. Sometimes they are
asked to make a prediction before taking measurements. If groups are running low on
time, advise them to build the circuit, take measurements and avoid the calculations and
analysis questions for the time being.
Students will build a circuit that gets progressively more complicated. The circuit
begins with one resistor. Another resistor of the same resistance will be added in parallel;
then, a third resistor of the same resistance will be added in parallel. The last (fourth)
circuit is no different than the third, but instead of having the three parallel resistors of
equal resistance, the students switch two of the resistors so that all three resistors are
different. For each circuit, students will measure current, voltage, calculate resistance
using Ohm’s Law, and calculate the equivalent (total) resistance in the circuit.
Homework
Complete all calculations and answer the analysis questions for Part 1 and Part 2.
Day 3: Discussion
Use this day to discuss the students’ findings about series and parallel circuits. Drawing a
circuit diagram may be of assistance.
1. Series Circuits: Current is the same through each resistor – only one path
therefore the traffic/flow is always the same.
IPS = I1 = I2 = I3 = …
2. Voltage: depends on the resistance of the resistor. Larger resistor needs more push
for e- to travel through. Voltage from the source (VPS) equal to sum of the
voltages across each resistor.
VPS = V1 + V2 + V3 + …
3. Resistance: Equivalent resistance (Req) appears to be the sum of the individual
resistances.
Prove using Ohm’s Law:
VPS = V1 + V2 + V3 + …
V=IxR
IPS(Req) = I1 (R1) + I2 (R2) + I3 (R3) + …
Since I is the same throughout, then
Req = R1 + R2 + R3 + …
4. Parallel Circuits: Voltage is the same across each resistor – same potential over
each parallel branch
VPS = V1 = V2 = V3 = …
5. Current: depends on the resistance in the branch. The total current (all the
branches when they are together either before a split or after they reconnect) is
equal to the sum of the current through each parallel branch.
IPS = I1 + I2 + I3 + …
6. Resistance: The equivalent resistance is less than the resistance of each of the
individual resistors. For two resistors of the same resistance, it appears to be half
the individual resistors. For three resistors of the same resistance, it appears to be
one third of the individual resistors. It is more difficult to determine this when all
the resistors are unequal.
Prove using Ohm’s Law:
IPS = I1 + I2 + I3 + …
I=V/R
VPS/Req = V1/R1 + V2/R2 + V3/R3 + …
Since V all the same across each resistor, then
1/Req = 1/R1 + 1/R2 + 1/R3 + …
Show the students how this works with their experimental values.
After the class discussion, debrief the students on their knowledge of Scientific
Inquiry and the aspects of the Nature of Science. When debriefing the students, refer to
your charts posted in the classroom. Probe the students on which aspects of the Nature of
Science were applicable in this lesson. Refer to the lists at on the first page of the model
lesson. The students should be able to come up with most, if not all, of the items on the
list. If a student identifies an item that is not on the list, but has a rationale or justification
for including it, then include this item, too.
Extensions
Provide students with different circuits. Ask them to determine the total current that
would travel through the circuits and the current through each resistor.
Assessment
1. As the students are building the circuits, the teacher will walk around the room to
make sure the students are following directions.
2. For the computations and analysis questions, assessment can be broken into two
areas: computational skill and conceptual understanding. Some of the work in
this lesson requires students to make fairly straightforward computations using
Ohm’s Law. These parts can become a check on students understanding. Other
parts ask students to reflect on the process.
Modifications/Accommodations:
This is a hands-on lab, and is well-suited for English language learners, or
students whose language skills are poor.
Students who are visually impaired will have difficulty with this lab, and should
be paired with a non-visually impaired student.
Attachment
Lab worksheet
Name: _____________________________
Ohm, Ohm on the Range
Part I – Series Circuit
Purpose: To determine the relationship between the current and the voltage across the
resistors in series circuits.
Required Equipment/Supplies:
4 Digital Multimeters (1 voltmeter, 3 ammeters)
6 V voltage source
3 resistors of different resistance
wires
Discussion: Resistors can be connected end to end (in series) in a circuit. What is the
total resistance in the circuit and the voltages across the resistors? This experiment
explores these questions.
Procedure:
Step 1: Compute resistance for a simple circuit
Connect the largest rated resistor and an ammeter in series with the voltage
source. Connect a voltmeter across the resistor, as in the circuit diagram in Figure
A. (The resistance of the resistor is labeled R1. The two meters are shown as
circles with A for ammeter or a V for voltmeter.)
Measure the current (I) through the resistor and the
voltage (V) across it. Record your measurements.
Compute the resistance (R1) using Ohm’s Law.
1.
2.
3.
4.
What is the current (I) through the resistor? ____________________________
What is the voltage (V) across the resistor? _____________________________
Use Ohm’s Law to compute resistance R1. What did you get? ______________
How does your computed value of the resistance compare to the manufacturer’s rated
value?
Step 2: Add a second resistor.
Modify the circuit to include a second resistor of different resistance in series, as in the
diagram in Figure B. Record the manufacturer’s rating for each of these two resistors.
5. Before taking measurements, predict whether the current measured by ammeter A1
will be greater then, less than, or the same as the current measured in Step 1. Why do
you think this will be so?
6. What is the voltage (V) across the resistor? ______________________
7. How does your computed value of the resistance compare to the manufacturer’s rated
value?
8. Before taking measurements, predict whether the voltage across the resistor used
earlier in Step 1 will be greater than, less than, or the same as it was in Step 1. Why
do you think this will be so?
9. Measure and record the actual currents through each resistor (I1, I2) and from the
voltage source (I3), and voltages across each of the two resistors (V1, V2) and across
the two resistors (V3).
a) I1 = ______________
b) I 2 = ______________
c) I3 = ______________
d) How do the three current readings compare?
e) V1 =_____________
f) V2 = _____________
g) V3 = _____________
h) How do the three voltage readings compare?
Step 3: Compute the resistances.
Compute the values of resistances (R1, R2). Show your work.
Using Ohm’s Law, compute the equivalent resistance (Req) of the two resistors
using the current leaving the voltage source (I3) and the voltage across the two
resistors (V3).
a) R1 = _____________
b) R2 = _____________
10. How does this equivalent resistance (Req) compare to the sum of the resistances of the
two resistors that you computed (R1, R2)?
Step 4: Predict current for three resistors.
Again modify the circuit to include a third resistor of different resistance in series,
as in the diagram in Figure C. Record the manufacturer’s rating for each of these
three resistors.
11. Measure the voltage across the three resistors. V4 = ______________
12. From the manufacturer’s ratings and your observations from Step 3, what should be
the total resistance of the circuit? ___________________
13. Before taking any measurements, predict what the three ammeters in Figure C will
read.
a) A1: ___________________
b) A2: ___________________
c) A3: ___________________
Step 5: Measure the currents and voltages.
Measure the currents on each of the ammeters in Figure C (I through A1, A2, A3)
and use your voltmeter to measure the voltage across each resistor (V1, V2, V3).
14.
a) A1: ___________________
b) A2: ___________________
c) A3: ___________________
d) V1 =__________________
e) V2 = __________________
f) V3 = __________________
15. How do your measured values of the current through ammeters A1, A2, and A3
compare to the values you predicted in Step 4?
Step 6: Compute the resistances.
Compute the values of resistances R1 R2, and R3. Show your work.
Using Ohm’s Law compute the equivalent resistance (Req) of the three resistors
using the current leaving the voltage source (I3) and the voltage across the three
resistors that you measured (V4).
16.
a) R1 = __________________
b) R2 = __________________
c) R3 = __________________
17. How does this equivalent resistance (Req) compare to the sum of the resistances of the
three resistors that you computed (R1, R2, R3)?
Analysis:
1. Describe how the currents in different parts of a series circuit compare.
2. Describe the relationship between voltage of the source (across all of the
resistors) and the voltages across each resistor in a series circuit.
3. Describe the relationship between the sum of the resistances and the sum of the
voltages across each resistor.
Part II –Parallel Circuit
Purpose:
To determine the relationship between the current and the voltage across the
resistances in a parallel circuit.
Required Equipment/Supplies:
5 Digital Multimeters (1 voltmeter, 4 ammeters)
3 V voltage source
3 resistors of equal resistance (10 Ω)
2 addition resistors of different resistance
wires
Discussion:
When electric current takes a variety of paths in going from one place to another,
we have a parallel circuit. Ohm’s Law takes on added interest in such a circuit.
Procedure:
Step 1: Compute resistance for a simple circuit
Connect a 10 Ω resistor and an ammeter in series with the voltage source.
Connect a voltmeter across the resistor, as in the circuit diagram in Figure A. (The
resistance of the resistor is labeled R1. The two meters are shown as circles with
A for ammeter or a V for voltmeter.)
Measure the current (I) through the resistor and the
voltage (V) across it. Record your measurements.
Compute the resistance (R1) using Ohm’s Law.
1. I = _________________
V = ________________
R1 = _______________
Step 2: Add a resistor in parallel.
Place a second 10 Ω resistor (equal resistance) in parallel with the first resistor, as
in the diagram in Figure B. Also add additional ammeters so that the current
through each resistor (A1, A2) and from the voltage source (A3) as shown in Figure
B.
2. Before taking measurements, predict whether the current measured by ammeter
A3 will be greater then, less than, or the same as the current measured in Step 1.
Why do you think this will be so?
3. Before taking measurements, predict whether the voltage across the resistor used
earlier in Step 1 will be greater than, less than, or the same as it was in Step 1.
Why do you think this will be so?
4. Measure and record the actual currents through each resistor (I1, I2) and from the
voltage source (I3), and voltages across each of the two resistors (V1, V2) and
across the two resistors (V3).
a) I1 = ______________
b) I2 = ______________
c) I3 = ______________
d) V1 = _____________
e) V2 = _____________
f) V3 = _____________
5. How do the three current readings compare?
6. How do the three voltage readings compare?
Step 3: Compute resistances.
Compute the values of resistances (R1, R2). Show your work.
Using Ohm’s Law, compute the equivalent resistance (Req) of the two resistors
using the current leaving the voltage source (I3) and the voltage of the source (V3).
7.
a) R1 = _______________
b) R2 = _______________
c) R3 = _______________
8. How does this equivalent resistance (Req) compare to the two resistors that you
calculated (R1, R2)?
Step 4: Add a third resistor in parallel.
Add a third 10 Ω resistor (equal resistance) in parallel with the first and second
resistors, as shown in Figure C. Also add an additional ammeter as shown.
Measure and record currents on each of the ammeters (I through A1, A2, A3, A4)
and use your voltmeter to measure the voltage across each resistor (V1, V2, V3) and
the source (V4).
9.
a) A1: ___________________
b) A2: ___________________
c) A3: ___________________
d) A4: ___________________
e) V1 =__________________
f) V2 = __________________
g) V3 = __________________
h) V3 = __________________
Step 5: Compute the resistances.
Compute the values of resistances R1 R2, and R3. Show your work.
Using Ohm’s Law compute the equivalent resistance (Req) of the three resistors
using the current leaving the voltage source (I4) and the voltage across the three
resistors that you measured (V4).
10.
a) R1 = _______________
b) R2 = _______________
c) R3 = _______________
11. How does this equivalent resistance (Req) of the circuit compare to the three
individual resistances that you computed (R1, R2, R3)?
Step 6: Repeat using different resistors.
Repeat Step 4 using three resistors of unequal resistance. Measure and record
currents on each of the ammeters (I through A1, A2, A3, A4) and use your
voltmeter to measure the voltage across each resistor (V1, V2, V3) and the source
(V4).
12.
a) A1: ___________________
b) A2: ___________________
c) A3: ___________________
d) A4: ___________________
e) V1 =__________________
f) V2 = __________________
g) V3 = __________________
h) V3 = __________________
Step 7: Compute the resistances.
Compute the values of resistances R1 R2, and R3. Show your work.
Using Ohm’s Law compute the equivalent resistance (Req) of the three resistors
using the current leaving the voltage source (I4) and the voltage across the three
resistors that you measured (V4).
13.
a) R1 = _______________
b) R2 = _______________
c) R3 = _______________
14. How does the equivalent resistance (Req) compare to the three individual
resistances that you computed (R1, R2, R3)?
Analysis:
4. Describe how the currents in different parts of a parallel circuit compare.
5. Describe the relationship among voltages in parallel branches of a circuit.
6. Describe the relationship between the equivalent resistance and the individual
resistances of each resistor in a parallel circuit.