Concept Presentation:
Ohm’s Law
Presenter: Jon Martin
Mentor: Ann Hu
Presentation Outline:
• Background Information
• Curriculum Expectations
• Misconceptions/Learning Styles
• Demonstrations
• Unit/Lesson Sequence/Teaching Ideas
• Assessment/Learning Styles
• Practical Applications
• Annotated References
Doesn’t everyone know the Ohm song?
http://www.youtube.com/watch?v=5nz2BjgDHvA
Q uickTim e™ and a
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Background Basics:
• Students entering grade 9 come from varying education
and schooling
• Possible misplaced students in academic or applied
courses
• Set the foundation of their science high school education
What is Ohm’s Law?
• Part of the grade 9 physics unit discusses current electricity
and introduces circuits
• Ohm’s Law is a quantitative formula relating voltage, current,
and resistance in electric circuits
• V (volts) = I (amperes) x R (ohm’s)
Curriculum Expectations:
• E2. investigate, through inquiry, various aspects of electricity, including
the properties of static and current electricity, and the quantitative
relationships between potential difference, current, and resistance in
electrical circuits.
• E2.8 solve simple problems involving potential difference V, electric
current I, and resistance R, using the quantitative relationship V = IR [AI,
C]
• E3.5 explain the characteristics of electric current, potential difference,
and resistance in simple series and parallel circuits, noting how the
quantities differ in the two circuits
Curriculum Expectations Cont’d:
• E3.6 describe, qualitatively, the interrelationships between
resistance, potential difference, and electric current (e.g., the effect on
current when potential difference is changed and the resistance is
constant)
•E3.8 explain how various factors (e.g., wire length, wire material,
cross-sectional area of wire) influence the resistance of an electrical
circuit
Misconceptions:
- What we find simple, students find incredibly challenging.
We must attempt to think back to times when we also
struggled with similar concepts, and appreciate even the most
seemingly trivial concept can be excruciating for certain
learners
Misconception #1:
“Is there a difference between voltage and potential difference?”
• Often students confuse these two terms due to the common
interchanging of them in science
• Explain voltage is energy per unit charge while potential
difference is the amount of energy ‘used’ between two points in a
circuit.
• “Marshmallow circuits” (Nick’s Best Practice)
Misconception #2:
Students assume resistance must come from resistors.
• Explain that all loads in a circuit will have some value of
resistance.
• Remind students that energy is neither created nor
destroyed, but can be converted. Resistance is the
conversion of energy into light, sound, heat, etc.
An analogy for resistance:
Potential
Energy Gained
Energy converted
into heat through
friction
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Quic kTime™ and a
TIFF (Unc ompres sed) dec ompres sor
are needed to see this pic ture.
Q uickTim e™ and a
TI FF ( Uncom pr essed) decom pr essor
ar e needed t o see t his pict ur e.
Q uickTim e™ and a
TI FF ( Uncom pr essed) decom pr essor
ar e needed t o see t his pict ur e.
Quic kTime™ and a
TIFF (Unc ompres sed) dec ompres sor
are needed to see this pic ture.
Kinetic Energy
of Motion
Misconception #3:
“Why is resistance different in series versus parallel circuits?”
• Student activity: Straws and air resistance (analogy)
• This is a good time to remind students that the factors that affect
resistance are cross-sectional area, length of wire, and wire
material. Which of these factors came into play in the previous
activity?
• How might this activity be modified to be less instructive?
Misconception #4:
Students will often confuse the symbols
of Ohm’s Law and forget how to derive
the proper formulas depending on the
unknown being asked for.
Q uickTim e™ and a
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• Introduce the equation triangle
• Sample DI
• What other modifications can you
think of for the applied learner?
Misconception #5:
Students mistake the terms ‘open’ and ‘closed’ when referring to
circuits.
• It is common sense to believe open allows things to flow, and
closed means the prevention of movement, like a door allows people
to enter while open, and prevents people from moving through
while closed. This is an important note to make especially for ELL
students
• Use the analogy of a draw-bridge that while closed, allows cars to
travel over it, but if it is opened (raised) the cars can no longer travel
across.
Closed bridge means cars can move
Q uickTim e™ and a
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Open bridge means cars must stop and wait
Q uickTim e™ and a
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Curriculum within the Unit:
• The grade 9 physics unit is typically taught as the 3rd or 4th
unit in the curriculum
• Within this unit, Ohm’s Law should be taught after the
concepts of voltage and current are well understood. The
students should also have a good understanding of drawing
and interpreting circuit diagrams
Lesson Sequence:
Lesson 1
- Discuss circuit symbols and have students draw and identify
them. Show the students the real instruments so they make
connections with real objects and the symbols they have
learned.
- Assessment for learning
- Students can peer (and self) assess one another using
flash cards with circuit symbols and definitions of terms
- MI: logical, tactile, kinesthetic, intra/interpersonal, visual
Lesson 2
- Introduce series circuits to students and basic voltage and
current calculations.
- Allow students to investigate building small series circuits
with lab materials
- Assessment for learning
- Exit pass
- MI: logical, tactile, kinesthetic, intra/interpersonal, visual
- ELL students may require extra diagrammatic aid
Lesson 3
- Advance students to parallel circuits and basic voltage and
current problems
- Allow students to investigate building small parallel circuits
using lab materials
- Assessment for learning
- 3 minute questions
- MI: logical, tactile, kinesthetic, intra/interpersonal, visual
Lesson 4
- Review with “Marshmallows and circuits” activity reinforcing
potential differences of loads in series versus parallel circuits
- Introduce the concept of resistance, factors that affect
resistance, Ohm’s Law and the equation triangle
- Allow students to attempt basic mathematical calculations
using the concepts of voltage, current, and resistance
- Assessment for learning
-Mini-quiz
- MI: logical, tactile, kinesthetic, intra/interpersonal, visual
Lesson 5
-Begin with air resistance student activity
-Remind students of the factors that affect resistance in wires
-Move into circuit building activities in which students will build
more complicated series and parallel circuits, and demonstrate
more advanced understanding of observing and measuring
voltage, current, and resistance.
- Assessment of learning
- Lab Report
- MI: logical, tactile, kinesthetic, intra/interpersonal, visual
- ELL students may require extra diagrammatic aid
Lesson 6
- Circuit building online computer simulation
- Move students into computer lab or library/resource center
http://phet.colorado.edu/simulations/sims.php?sim=Circuit_Constru
ction_Kit_ACDC
- Assessment for learning
- Checklist
- MI: logical, tactile, kinesthetic, intra/interpersonal, visual
Safety Considerations:
• Very few safety considerations for this portion of the unit.
• The electrical devices have limited voltage
• There is always a slight chance of shock so remind
students to avoid contacting the opposing terminals of the
battery.
• Remind students why it is unsafe to place conducting
objects near or into electrical outlets, as these circuits have
a much higher voltage.
Applications and Societal Implications:
• Understand why energy is lost in forms of heat, and
light, and sound, as electrons lose energy to loads
(resistors) within circuits, e.g. buzzers.
• Relate resistance to a number of other everyday ideas
such as drinking through straws.
• Resistors are also everywhere! Almost every electric
circuit has them to ensure the current does not exceed the
component value. IPods, cell phones, PSPs! Try living
without those for one day!
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Annotated References:
James, E., Hirsch, A., Plumb, D., Ritter, B. (1999) Nelson 9, Toronto:
Thomson Canada Limited
This resource was helpful in providing useful teaching material and
ideas for the curriculum and lesson planning.
ON Science 9. McGraw-Hill Ryerson Teacher’s Resource CD-ROM.
2009.
This resource is excellent for BLM’s as well as common misconceptions
for grade 9 topics in the Ontario curriculum.
Website: YouTube
http://www.youtube.com/watch?v=5nz2BjgDHvA
This song is a corny but catchy introduction to Ohm’s Law.
Website: Science Teachers Association of Ontario (STAO)
http://staoapps.com/e-lesson5.asp
This video is an instructional tool for teachers demonstrating the
difference in resistance between series and parallel circuits.
Website:
http://phet.colorado.edu/simulations/sims.php?sim=Circuit_Construct
ion_Kit_ACDC
This web resource allows students to quickly and easily manipulate
circuit diagrams and observe and record various scenarios they can
come up with themselves.