Honours Specialist General Science

Honours Specialist General Science

Concept Presentation

SNC1D

Grade 9 Academic Science

Ohm’s Law

Jon Martin

Thursday, July 15th, 2010

Mentor: Ann Hu

Instructors: Janine Extavour, Marty Zatzman

Background information:

Students entering grade nine academic science have been streamed into the class based on grade eight results. These students are very often new to this school and have a very low understanding of how the science program is run at the high school level. These students may also have been mis-placed; meaning some would be better suited moving from 9 academic to 9 applied, and vice versa. Therefore teaching a grade nine applied or academic class can be challenging, as the class will often have an diverse range of learners, as well as varying academic backgrounds depending of the feeder schools they attended. It is therefore important that a strong base is founded in the grade 9 curriculum, as this is the stepping stone for students to make choices whether to take other science courses in their future.

The purpose of this unit is for students to discover the differences between series and parallel circuits, to understand key vocabulary such as voltage, current, and resistance, and to develop a basic understanding of Ohm’s Law and the mathematical equations related to this topic. This concept presentation will explore Ohm’s Law in greater depth, and discuss common misconceptions and roadblocks students might encounter, as well as accommodations/alternative teaching strategies to meet the needs of the diverse classroom learners.

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.

E3. Demonstrate an understanding of the principles of static and current electricity.

E2.1 Use appropriate terminology related to electricity, including, but not limited to: ammeter, amperes, battery, current, fuse, kilowatt hours, load, ohms, potential difference, resistance, switch, voltmeter, and volts. [C]

E2.3 Predict the ability of different materials to hold or transfer electric charges (i.e., to act as insulators or conductors), and test their predictions through inquiry [IP, PR]

E2.5 Design, draw circuit diagrams of, and construct series and parallel circuits (e.g., a circuit where all light bulbs will go out when one light bulb is removed; a circuit that allows one of several light bulbs to be switched on and off independently of the others), and measure electric current I, potential difference V, and resistance R at various points in the circuits, using appropriate instruments and SI units [IP, PR, AI, C]

E2.7 Investigate the quantitative relationships between current, potential difference, and resistance in a simple series circuit [PR, AI]

E2.8 Solve simple problems involving potential difference V, electric current I, and resistance R, using the quantitative relationship V = IR [AI, C]

E3.1 Identify electrical quantities (i.e., current, potential difference, resistance, and electrical energy), and list their symbols and their corresponding SI units (e.g., electrical current: I, ampere)

E3.4 Identify the components of a simple DC circuit (e.g., electrical source, load, connecting wires, switch, fuse), and explain their functions

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

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/Learning Gaps:

Roadblock #1

“I still don’t understand what potential difference means.”

The term potential difference can often throw students off, as the definition can be very wordy. Voltage is often defined as the difference in electrical potential between two points in a circuit. This definition can be quite confusing, even for highly educated individuals, and so we must find a way to form an analogy for the students to understand. A great activity for this roadblock is the “Marshmallow Circuit.” Refer to Nick’s “Best Practice” for a detailed outline of the activity and materials required. This activity is a great accommodation for tactile/kinesthetic learners.

Roadblock #2:

Students assume resistance must come from resistors.

It needs to be carefully explained to students that resistance can be thought of as the “difficulty” of flow for electrons through any load in the circuit. Explain to students that a load could be something such as a light bulb, or an appliance, or a specially designed resistor. All loads will impede the flow of electrons in a circuit to some degree. Refer to online virtual circuit activity for examples. This activity is an excellent accommodation for visual learners.

Roadblock #3:

“Why is resistance different in series vs. parallel circuits.”

Reinforce to students that resistance is much higher series than in parallel circuits.

Student Activity:

Comparing resistance in series and parallel circuits

Materials:

6 small straws

Small section of masking tape

Take one of the small straws and try blowing through it. Now take a piece of masking tape and connect two straws end to end so that they are connected smoothly and that air could still pass through each of them. Take a third straw and a small piece of masking tape and again connect it to the other two connected straws as you did above. Your three straws should be connected as loads in “series” with one another. Now try blowing through the three connected straws.

Was this easier or harder than before?

Take the remaining three straws and line them up parallel to one another instead of linearly as you did last time. Use the remaining tape to connect these straws side by side. We can imagine that these straws are connected to each other in “parallel.” Now try blowing through these three straws.

Was this easier or harder than blowing air through the straws in ‘series?’

Which group of straws resisted the airflow the most?

This activity is an excellent modification for tactile learners.

Roadblock #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.

We all understand the benefit of equation triangles in both math and science. The three formulas related to Ohm’s Law are:

V = IR I = V/R R = V/I

The equation triangle reduces the amount of memorization students have to do, and reminds them when to multiply and when to divide variables.

V

I R

Simply put, the horizontal line acts as a division symbol, where the vertical line acts as a multiplication symbol. This graphic organizer can be used throughout their science and math courses for various three variable equations.

Roadblock #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. 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. This is an important note to make especially for ELL students.

Advanced Unit Preparation:

-  Potential difference activity materials must be gathered (mini marshmallows, clear plastic cups). Summary of activity worksheets photocopied.

-  Online visual circuit demo requires a laptop and projector. If this is used as a student lab or activity, a computer lab or library would have to be booked in advance. Student activity directional worksheets photocopied.

-  Differences in resistance in series vs. parallel circuits activity materials must be gathered (Per student group; 6 small cocktail straws, masking tape). A student handout must be also be photocopied.

-  Handout explaining Ohm’s Law and the equation triangle with varying student practice problems must be photocopied.

-  All required materials for circuit building must be available and functional (i.e., have adequate number of working bulbs, batteries, connecting wires, resistors, voltmeters, ammeters etc.).

-  All other student handouts, activities, quizzes etc. must be photocopied.

Lesson Sequence and Teaching Ideas:

Topic / Ideas / Learning Style / Assessment
Lesson 1
Circuit symbols and vocabulary / - Discuss circuit symbols and have the students practice drawing the symbols themselves.
- Use flash cards with symbols and definitions for students to quiz each other with / Visual
Auditory
Tactile
ELL / Formative
Peer assessment
Self assessment
Lesson 2
Series circuit diagrams / - Introduce students to drawing circuit symbols in series circuit diagrams
- Discuss calculating total voltage and current in series circuits
- Have students attempt simple calculations using given circuit diagrams / Visual
Auditory
Tactile
ELL / Formative
Exit Pass
Lesson 3
Parallel circuit diagrams / - Advance students to drawing circuit symbols in parallel circuit diagrams
- Discuss calculating total voltage and current in parallel circuits
- Have students attempt simple calculations using given circuit diagrams / Visual
Auditory
Tactile
ELL / Formative
3 Minutes of questions
Lesson 4
Ohm’s Law / - Begin with “Marshmallows and Circuits” activity to reinforce student understanding of potential difference and the differences between series and parallel circuits
- Introduce concept of Ohm’s Law
- Simplify Ohm’s Law by giving the equation triangle
- Allow students to attempt basic mathematical equation manipulation using Ohm’s Law / Visual
Auditory
Tactile
Kinesthetic
ELL / Formative
Mini-quiz
Lesson 5
Circuit building activity / - Begin with small resistance activity using small straws
- Reinforce that resistance is difference in series and parallel circuits, and that this such as length of wire, wire material, cross-sectional area of wire) will all affect resistance
- Move into the circuit building activity in which students will build a number of circuits both series and parallel, and record voltage, current, and resistance / Visual
Auditory
Tactile
Kinesthetic
ELL / Summative
Lab Report
[IP, PR, AI, C]
Lesson 6
Circuit building virtual activity / - Move students to library or computer lab and have them carry out a variety of manipulations using the online virtual circuit builder / Visual
Tactile
ELL / Formative
Check-list

Safety Considerations:

There are very few safety considerations for this portion of the unit. The electrical devices they will be working with in the circuit building activities should have limited voltage, and could likely do little harm to the students. 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:

-  Understanding Ohm’s Law and resistance allows us to 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.

-  Resistors are used in heating elements as well as light bulb filaments.

-  Relate resistance to a number of other everyday ideas such as drinking through straws.

-  Resistors are also used in almost every electric circuit to ensure the current does not exceed the component value. IPods, cell phones, PSPs! Try living without those for one day!

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_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.