Concept Presentation: Ohm’s Law

1. Concept Presentation:Ohm’s Law Presenter: Jon Martin Mentor: Ann Hu

2. Presentation Outline: • Background Information • Curriculum Expectations • Misconceptions/Learning Styles • Demonstrations • Unit/Lesson Sequence/Teaching Ideas • Assessment/Learning Styles • Practical Applications • Annotated References

3. Doesn’t everyone know the Ohm song? http://www.youtube.com/watch?v=5nz2BjgDHvA

5. 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

6. 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)

7. 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

8. 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

9. 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

10. 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)

11. 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.

12. An analogy for resistance: Energy converted into heat through friction Potential Energy Gained Kinetic Energy of Motion

13. 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?

14. 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. • Introduce the equation triangle • Sample DI • What other modifications can you think of for the applied learner?

15. 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.

16. Closed bridge means cars can move

17. Open bridge means cars must stop and wait

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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_Construction_Kit_ACDC • - Assessment for learning • - Checklist • MI: logical, tactile, kinesthetic, intra/interpersonal, visual

25. 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.

26. 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!

28. 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.

29. 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_Construction_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.