Circuits: From Static to Moving Charges
Lesson 1 of 13
Objective: Students will begin to develop their intuition about the ways that charges move in electric circuits.
I ask students today to engage in a bit of creative fun. As part of a two-part warmup, I first ask them to try to list 3-5 examples of the conservation of energy. Though students may not be aware, we've invoked this principle nearly every day in class. With this exercise, I'm hoping to make that more evident.
Once they have their list, I ask them to collaborate with 1-2 other students to create a tweet, pretending that they've just discovered this principle and wish to announce it to the world. In addition to creating the tweet, I ask students to develop a twitter handle and add in a hashtag that will make the tweet "trend worldwide." These elements add a bit of levity to the task and tend to open up the thinking.
After a three-minute window to create their lists, I give students about five minutes to generate the tweet and another five minutes or so to share their works. My hope is to create a memorable moment about the conservation of energy that is not, in any way, tied to a computational model. Many students actually access their Twitter accounts to confirm that their entry meets the 140-character limit. One student decided the world needed to know: here's her tweet.
Prior to this class, students have been preparing simple, short demonstration of electrostatic phenomenon. In a previous class, they rehearsed and some students volunteered to show their demos today.
I have asked students to take on this task for a variety of reasons. First, one of my failings as a teacher is that I am terrible at demonstrations! Second, and more importantly, students both enjoy the process of finding and prepping a demo but also seem to internalize many of the fundamental concepts of charges while doing so. As a related note, the sense of fun and playfulness that accompanies this exercise goes a long way toward creating student ownership of the classroom.
Here, two students prepare a number of small bits of paper to be picked up by the charged balloon:
And, here, they are successful!
As with the previous demonstrations, I want my presenters to articulate the role that charged particles play in their demo. I want my student audience to appreciate the variety of ways that static charges can be witnessed and, to a limited extent, controlled or manipulated.
I gather students back to their seats to begin thinking about electricity and electric circuits. To get early student conceptions about circuits, I ask my students to engage in a two-minute "free write." They try to get whatever thoughts they have about "circuits" on paper. After this writing exercise, I ask them to turn to one another and share their thoughts. Now, having written, talked, and spoken about circuits, they are much more likely to contribute to the large class discussion.
I ask for students to shout out their ideas to me and I try to capture their thoughts on the board as rapidly as possible - this can lead to a messy situation! (A clean version is also provided.) We spend a few minutes looking over the results without needing to correct any ideas or comment on every one. The important aspect of this is to really see what our preconceptions are about the topic of circuits. While there are some responses that are just silly, many of the main vocabulary words associated with circuits are present in our list. What seems to be missing is any true sense of the meanings of those words.
After gathering their thoughts on the board, I call up a simulation which allows us to pursue some of the ideas generated in this segment of class. By using that simulation, we start the process of assimilating those vocabulary words into our learning.
After facilitating the student discussion of preliminary thoughts about circuits, I show my students a circuit simulation that allows them to build circuits with simple elements. At my Smartboard, I show the following screen and begin to introduce the features of the simulation.
The simulation starts off blank but includes a number of possible elements to populate the board. For example, students can build a simple circuit or anything more complex; I limit this segment of class to some simple variations.
The point of this activity is to stimulate students' thinking and to provide an opportunity for them to speculate about the influence of a variety of changes. Students have questions - "What happens when you ad another light bulb?" - but I try not to immediately provide answers. Instead, I use the simulation to create insight into student questions. For example, if a student wants to know what will happen to the brightness of the first bulb if we add a second one, I solicit student thoughts, then create the circuit at the board, and we observe any changes. I continually facilitate the discussion, looking for ways to touch upon the ideas of voltage and current. I also add in challenges, asking students to come to the board to, say, reverse the direction of the current in a given circuit.
The lesson ends with some intuition developed about voltage, current, and energy in a circuit. It is not the goal to have these concepts defined properly but, rather, to have them seem familiar for the work that lies ahead.