Household Circuits

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Objective

Students provide evidence for which type of circuit (parallel or series), is found in the wiring of their house.

Big Idea

In a series circuit, the current remains constant and voltage-drops add together and in a parallel circuit the current adds and voltage-drops are constant.

Context and Supplies

Based on the what students have learned about types of circuits from past lessons, Parallel and Series Circuits and Circuit Sudoku, students synthesize this information to provide an explanation on they type of circuit they find in a home or business. This applies to the CCSS English Language Arts literacy standard RST.11-12.9: Synthesize information from a range of sources (e.g., texts, experiments, simulations) into a coherent understanding of a process, phenomenon, or concept, resolving conflicting information when possible.

Students observe how the currents and voltages change in a series circuit and in a parallel circuit. They analyze the data and conclude what type of circuit their house must be. They cite evidence to support their conclusion. NGSS Science Practice 1: Asking questions, Science Practice 4: Analyzing and interpreting data, Science Practice 5: Using mathematics and computational thinking, Science Practice 6: Constructing explanations and Science Practice 7: Engaging in argument from evidence are involved in this process as are CCSS Math Practice 2: Reason abstractly and quantitatively and Math Practice 3: Construct viable arguments and critique the reasoning of others.

Since voltage is an electric potential due to electric fields, the performance standard HS-PS3-5: Develop and use a model of two objects interacting through electric or magnetic fields to illustrate the forces between objects and the changes in energy of the objects due to the interaction.

Adding a Resistor to Series and Parallel Circuits

20 minutes

I tell students today's objective is for them to supply evidence on the type of circuit their house has: parallel or series. In order to engage in this activity, they should create their own summary of these types of circuits. I instruct them to open their notebooks to a new page and divide that page in half with a pen. On one half of the page, they draw the table and schematic for the first circuit on the Circuit Sudoku Challenge. However, they should add a fourth,10 ohm resistor to the schematic and add a row to the table. On the second half of the sheet, they again add a fourth 10 ohm resistor to the second circuit on the Circuit Sudoku Challenge, which is a parallel circuit.

Then I have students spend 10 minutes to complete the new circuit and analyze the changes to the total current and resistance from the addition of the fourth resistor. As students complete their analysis, I call on several random students to each provide one feature of the circuit of their choice. I get responses such as:

• The parallel circuit voltage is the same across all resistors.
• The series circuit current is the same throughout.
• When a resistor is added to a parallel circuit, the total current increases!
• When a resistor is added to a parallel circuit, the total resistance decreases!

As students provide their features, I write them down on my own summary sheet on the Add a Resistor Overhead paper. I instruct all students to add a feature to their own notebook if they don't already have it.

When we are done, we have a good summary sheet of parallel and series circuits and what happens when you add a load, or resistor, to each.

Household Circuits - Series or Parallel?

10 minutes

I remind students that the potential difference for any plug in their house is approximately 120 volts and that most electronic devices, appliances and power supplies operate best when they have 120 volts across them.

I instruct students to get out a blank sheet of paper and have them write the prompt; "The wiring in my house is ____________ because...". In the blank they put either parallel or series and they are to supply at least three reasons for their conclusion. This is done in silence and solo by each student as I want them to look through their summary sheet and devise their own conclusions.

Students have 5 minutes to write their statement at which point I collect their sheets. I choose a few student samples to place under the document camera for the class to view. I make sure the samples provide correct and sensible answers as I don't want to embarrass students who make mistakes. The first example on this House Circuit - Student Work states that "if one light doesn't work then none will come on. (series)". I clarify that this is a reason why a household circuit is NOT series! We spend several minutes to list out the reasons why a household circuit must be in parallel. Here are the reasons that students supply.

In a parallel circuit:

• The voltage across all electrical devices is 120 volts
• The voltage doesn't change as you add more devices.
• If you turn off or remove one device, it does not turn off the whole circuit.
• If you add new devices, it does not change the voltage or current going through other devices on the same circuit.

As we go through this exercise, I encourage students to write these responses in their notebooks as they have an open note quiz at the end of the period.

Closing Quiz on Circuits

15 minutes

After we review a summary of both parallel and series circuits and the reasons that a house must be wired in parallel. It is now time for a quiz so that I can assess student understanding.

For the Circuits Summary - Quiz, I use a free online service called Socrative (one can upload this template into Socrative; Circuits Summary - Questions). Students use their smart phones to take the a multiple-choice quiz, if they don't have one, they are free to use a classroom laptop. I start the quiz and instruct the students to take the 14 question quiz. To reduce the occurrence of cheating, which is made easier with the use of their smart phones, I select a feature on Socrative where the questions and the answers are scrambled. This way, each students seated next to each other a unlikely to see the same questions at the same time. And even if they do see the same question, the answer order is different. The quiz takes about 12 minutes to take and most students finish it just as class ends.