Title of Activity: Let there be Light! Introduction to Ohm's Law and basic series circuits. Concepts Covered: Circuitry is in all of our electronics. This circuits must be asembled in specific ways to allow the load (light bulb in this case) to operate. Ohm's Law dictates various values for important information about the circuit. These values allow us to know how something will operate. Length of Lesson: 1 day (11th or 12th grade) Standards: National: 1 (Unifying Processes and Concepts); 2 (Science as inquiry); 3 (Physical Science, electricity); 6 (Science in technology); 7 (Science in personal and social perspectives) Colorado: 3.5 (Energy exists in many forms and is predictable and measurable, high school) Learning Objectives: SWBAT 1. Explain what variables stand for and how to manipulate the basic circuit formula V=IR 2. Define voltage, resistance, and current in writing. 3. Define open and closed circuits. Explain which is necessary to operate a load. 4. Define series circuit 5. Be able to diagram a simple circuit using accepted scientific symbols. 6. Make predictions/calculations using Ohm's Law, V=IR, about a loads resistance, an energy source's voltage and a circuits amperage. Materials: 6 D batteries, 6 copper wires, a roll of electrical tape, 6 ammeters, and 6 3v light bulbs. (6 groups) Planning: Have six cuts of copper wire ready to go as well as the batteries and little light bulbs, also, have the electrical tape in six pieces hanging on the end of each grouping of materials so students do not have to cut it themselves (saves time). Have the materials grouped together prior to class so that when it is time for the experiment, groups have quick access. Prepare discussion questions and conversation pieces prior to class. Come prepared with warm-up questions or a power point or something to get discussion started about the necessary theory and models. Safety: People could get shocked if they try to do something silly like stick the copper wires into an electrical socket. Remind the students to only use the batteries as power sources. Procedure/Activity: Engage Explore Student Activity Answer the warm-up prompt through discussion. Construct a simple circuit using the materials available. Teacher Activity Ask the warm up, what are electrical circuits? Where are they located? Name three objects that you use everyday that has electrical circuitry. What are the three main parts of an electrical circuit? Say, I m going to give you a battery, a bulb and a piece of
Investigate at least two ways to connect the three items (wire, battery bulb) that result in light and 2 ways to connect them that do not. Diagram all four of these configurations. wire. You have one task Make the bulb light. The only rules for this activity are that everyone participates, has an opportunity to touch the materials and all ideas are treated with respect. Don't give them any hints, let them struggle and help answer their questions as they arise. They should be figuring out a few things, the wire needs to be attached to both sides of the battery and bulb, or the bulb needs to be on one end of the batter while the wire attaches it to the other end of the battery. Explain Have students share some of their functioning diagrams After discussion, students will answer: Why did some configurations work and why did others fail? Students will redraw their diagrams. Partake in discussion of Ohm's Law, using his law, describe how you could predict the current in one of your circuits with the battery, light bulb, and copper wires. Write down calculated prediction of current and values measured for V and R. Bring the class back for discussion about how to make the circuit function. Display how to properly diagram a circuit using the accepted symbols. Have the students redraw their diagrams. Next move into a discussion with Ohm's Law. Explain the equation V=IR Pass out the ammeters and have the students reconstruct a functional circuit. Explain how to use the ammeter. Ask them how it would be possible to determine the current draw of the light bulb. (They will need voltage and resistance of the bulb this can be measured) Once this done they can predict the current using
Elaborate Students will notice that their predicted value and the value they measure is different. Record this. Have them explain why they might think this is. After discussion, make any changes to their initial thoughts about the reasons for the discrepancy. Students should write 2 to 3 sentences explaining the discrepancy. Ohm's Law, then connect the circuit and actually measure the current. The values ought to be different. Help the students use the ammeters when they are measuring current. Bring the class together one final time to discuss the reason the Current is different. Ask: If the voltage remained the same, and the current is different, what must also be different from your original measurements (resistance)? Have them calculate this new resistance. Begin a discussion about where this change in resistance could have come from. Evaluate Students will turn in 4 diagrams of initial circuitry investigation and will include their measured and predicted values for the circuit after using the ammeter. No formal lab write up necessary though there are required diagrams, calculations, and explanations to be turned in their science notebooks. Collect the four initial diagrams for the investigation into circuitry. Collect the final diagram including measurements and predictions of V, I, and R as well as the final recalculation of R along with a two to three sentence explanation of why R changed. Provide a rubric for the necessary information to be included in their notebook Assessment: Formative: Diagrams of initial circuitry investigation in notebooks, check for participation in class discussions. Summative: Diagrams and calculations for experiment involving ammeter in notebook.
Anticipated Misconceptions: 1.When an electrochemical cell no longer works, it is out of charge and must be recharged before it can be used again. 2. An electrochemical cell can be a source of charge in a circuit. The charge that flows through the circuit originates in the cell. 3. Charge becomes used up as it flows through a circuit. The amount of charge that exits a light bulb is less than the amount that enters the light bulb. 4. Charge flows through circuits at very high speeds. This explains why the light bulb turns on immediately after the wall switch is flipped. 5. The local electrical utility company supplies millions and millions of electrons to our homes every day. Accommodations/Modifications: It is possible to use something called "Snap Circuit Kits" in this lesson but as it is an introductory lesson they are not necessary. The kits come with instructions for circuit creation from basic to very complex but for this lesson you have to ask the students to avoid looking at those instructions. For the higher achieving students, offer them the chance to create a circuit with more than one light bulb and take measurement and calculations at differing locations on their new, more complicated circuit. For students that are struggling with the experiment or concepts, be sure to offer them assistance during experimentation. Usually it is a matter of motivation to try to solve the issue themselves rather than sheer inability to do the experiment. If there is still clear struggle, offer them the chance to omit the elaboration portion of the experiment because it is likely they will not get there during the lesson. That is ok because the main knowledge presented in the lesson and in the experiment comes in the initial set up in the explore and explain sections of the lesson. 1. Define the variable in Ohm's Law. Items Required in Notebooks 2. Define the three essential parts of a circuit, include the scientific symbols used to represent them in a circuit diagram. 3. 2 initial diagrams of a circuit that lights the bulb, 2 initial diagrams of a circuit that does not light the bulb. 4. label each of the diagrams in question one open or closed. (Think about the definition of a functional circuit) 5. Using the ammeter and Ohm's law, make a chart showing found/measured voltages and resistance as well as predicted current. Show the math necessary to predict this current. 6. Draw a diagram using the proper symbols of the circuit you are using your ammeter on. After making the prediction of the current, measure it, and include the measured current in your data chart.
7. With the measured current and the original voltage, calculate the new resistance. 8. Explain why the resistance changed and is not the original measured value.