Circuits: A Probe for Prior Knowledge Becomes a Lesson

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Objective

SWBAT explain how to make a simple series circuit using only a bulb, a wire and a battery.

Big Idea

The challenge is to find four ways to light the bulb with the wire and battery. Can you tell me where the wires from the bulb terminate inside the threaded portion?

The Need for This Lesson

We were about to take a closer look at electric motors and electromagnets when I decided to check for student understanding of basic circuits. You need to be able to complete a circuit to create both electric motors and electromagnets.

I selected a very easy pretest. I gave my students a wire, bulb and battery and asked them to light the bulb in four different ways. Not a single student was able to light the bulb.

Typically, the simple circuit is taught in 4th grade. The time between 4th and 7th grade is significant if you have no reason to revisit electricity. We know that the brain of the middle school student goes through significant changes. The students simply cannot remember how to create the circuit.

This lesson quickly brings students up to speed so we can explore middle school standards. In fact I gave the pretest, then transitioned to a lesson in one class period.

Investigation Preparation & Summary

10 minutes

Investigation Preparation & Summary

Before we can successful fully explore electric motors and electromagnets (MS-PS2-3 Ask questions about data to determine the factors that affect the strength of electric and magnetic forces.) I use this lesson to check for prior knowledge. Can my students complete a simple circuit?

Students are challenged to find 4 different ways to light a bulb using only a wire and a battery. for students with the prior skill set to light the bulb once with the wire and battery, this added challenge will help them extend their thinking and observations of patterns to develop additional solutions.

Students will plan and carry out an investigation (SP3 Planning and carrying out investigations) to find 4 different ways to light a bulb using only the bulb, a single wire and a battery. The drawings will be used to explain why it is possible to light the bulb 4 different ways. (SP6 Construct an explanation using models or representations. Students use their drawings to determine where the wires in the bulb terminate once inside the enclosed threaded part of the bulb. (SP2 Develop and/or use a model to predict and/or describe phenomena.) Students explain to others how observations of their scientific drawings leads them to conclude the termination points of the wires inside the threaded portion of the bulb. (SP7 Engaging in Argument from Evidence)

I prepare the lengths of wire ahead of class. I have found a good wire length to be about 30 cm. The ends will be stripped before student use to avoid wait time for the wire strippers. A complete materials list can be found in the resources section.

Students in Action

30 minutes

Students in Action

I pass out the materials to make a simple circuit. To my surprise, none of my students are successful. I hear a muttering or two about the wire getting too hot and realize that this check for prior knowledge needs to turn into a lesson. 

I stop the students and explain the lesson. Fortunately I suspected that we might need to review series circuits so I am prepared.

First I model for students how to draw each of the components of the circuit using the document camera. Sometimes my students get hung-up on drawing in their science journals so I try to simplify the effort by sharing some preliminary instructions.

In this video, I share my instructions for drawing the components of the circuit. This lesson is about making the circuits and not about drawing so I keep it simple. Attending to precision is going to be an important part of the student work in order to answer the challenge question at the end.

Their quest is to identify four different ways to light the bulb, document their findings in their journal. The challenge question asks students to use their drawings to infer what happens to the wires in the bulb when they enter the silver threaded part of the bulb - the part we cannot see.

The students have already complained about the wire getting too hot. This lets me know that they need to step back and think about what exactly a circuit is before I allow them to continue. We do not want students heading to the nurse from burns.

Since they have not yet been successful, we talk about what exactly is a circuit. I say that circuit reminds me of circle. To complete a circuit, we need to form a circle.

I explain when we stand in a circle, we can close the circle by holding hands. My left hand holds the hand of the person to my left and my right hand holds the hand of the person to my right. Each person in the circle holds the hand of two different people. In our circuit we need to make sure that each component touches two different parts of the circuit to form a circle. For example, the wire cannot touch both sides of the battery. This would be the same as forming a circle with only two people.

Two components cannot touch the same thing in the same place - the battery and the wire cannot both touch the bottom of the light bulb. This would be like skipping a person in the circle and two people touch the same hand of a third person. I am modeling this with a group of students so they understand.

Students begin their quest to light the bulb again. They discuss the holding hands example when the circuit doesn't work.

Only a few groups need additional help.

The first lighting of the bulb is now obvious but they are stymied when trying to find three more ways to light the bulb. I let students struggle for several minutes.

As I walk around the room, I ask students if the bulb always has to be on the positive side of the bulb. This helps.

Next I ask if the bulb always has to stand up on the battery. This takes students a few minutes to ponder before they understand the the bulb can be placed on its side.

I gently remind students that the bulb can be place on either the positive or negative side of the battery.

Finally students are answering the challenge question. There are several guesses. I tell them that the answers is clear if they carefully examine the drawings. Again I let students struggle for several minutes. Many find the answer as they discuss the drawings. I walk through the drawings with student groups sill struggling.

Connecting the Learning

20 minutes

We conclude this lesson by first checking our answers to the challenge question - Use the drawings you have just made to show what happens to the wires when they enter the enclosed threaded section of the bulb. Check! We are all good to go!

I ask students to reflect upon this lesson. Their answer - it was hard but it was fun, challenging but they could still figure it out. Mission accomplished! I tell students that a little frustration means they are learning. When they have a lot of frustration they need to ask questions. This lesson they conclude was just right. We had hints when we needed them but most of the time we were on our own.

We have a few minutes of class remaining, so I direct students to the PhET Circuit Simulation to practice making circuits with multiple bulbs and batteries. I like the PhET Simulations because they are inquiry based and quick to access. Students can connect their concrete experiences to virtual representations.

PhET Circuit Simulation