I’ve been taking a more inquiry-based, qualitative approach to labs and demonstrations. Based on my readings of Knight and Arons, assuming that students have any conceptual understandings of the core concepts in electrostatics would be a mistake. Common alternative conceptions include not identifying charge as a quality of an object, but rather as indistinguishable from the object, not distinguishing between charge and motion of charge, thinking of positive charge as an excess of protons, and many more. Further complicating this is that electrical phenomena is difficult to visualize. What is electrical potential anyway? Like, what is it really? Honestly, I didn’t fully grasp the concepts myself into well after two junior-level college courses in electrostatics and dynamics.
All of this screams at me that it is essential for students to have direct experience with the core concepts of electricity. How can they hope to understand charging by induction or the difference between conductors and insulators (beyond reciting textbook definitions) if they don’t have a solid understanding of what electrical charge is? Electrostatics is so much more than Coulomb’s Law, and it’s my goal to have my students exit this unit with understandings that I didn’t have even after finishing my B.S.
I got the inspiration for this from a set of Modeling documents on electrostatics. I had groups of 2-3 students set up two sets of these scotch tape “sandwiches.” (Click the picture to enlarge).
The top, base, and bottom are separate pieces of tape with handle-like “flaps” to make it easier to peel them off.
To record data and observations, students used 2′ x 2′ whiteboards that I keep for various purposes like this. I had them split their whiteboards into 4 sections, like this (click the picture to enlarge):
The purpose of each section is as follows:
- Experiment – Which two tapes are you looking at? TT for top-top, MM for middle-middle, BB for bottom-bottom. NOTE: The first picture above uses top-bottom-base. I did top-middle-bottom. Nothing more than a different preference for naming.
- Observe – Write observations about each pair of tapes before pulling and comparing.
- Predict – What do you think will happen?
- Describe – What did you see?
So, now what?
Since this was my students’ first “official” experience with electrostatics, I didn’t have them predict the first experiment. Predictions should be based on something; otherwise, they’re guesses, and I don’t think that carries much educational value.
The first part was simple. I just had the students pull the two top tapes and slowly bring them closer together (sticky sides facing each other). Exclamations such as “Woah!”, “What’s goin’ on here, Mr. Register?!”, and “MAGIC!” instantly convinced me that this was an excellent idea.
Once they were done playing with their top tapes, they wrote in the “Describe” box what they saw. Nothing fancy, just a few words.
Next, they wrote observations about the two tapes. What about the tapes were the same? What about them were different? I’ve found that it’s important to reinforce to students that there are no right or wrong “answers” here. Just write what you observe, and we’ll sort it out later. This can be difficult for students that have been trained and drilled to be answer-driven. However, they all catch on rather quickly! I then went group-by-group and had them share one observation each, and I wrote each of them on my SmartBoard.
To finish up, I had them follow the “proper” order for the middle-middle tapes and the bottom-bottom tapes. That is, take observations, predict, and then describe what they saw.
The Most Important Thing (TM)
What I’ve discovered is that the most important part of labs and demonstrations like this is that students use their observations to make meaningful predictions. A prediction that’s not based on observations and past results is nothing more than a guess. The idea is for me to choose experiments and experiences and to ask the right questions such that students begin building a mental model for explaining electrostatic phenomena. For this activity, the hope is that students would notice that subjecting the tapes to similar conditions produces similar results. The top tapes are both on top of another piece of tape as are the middle tapes. Both sets of tapes repel. Viola!
Part of this process for the students is to also filter out observations that don’t affect the outcomes. I wasn’t careful to make the tapes the same length, and students will notice that. Some students wondered if the direction of the tape handles had anything to do with the results. In true inquiry fashion, instead of giving the answer, I asked students what they thought and how they thought they could test it. This is great for those groups that work quickly and have nothing else to do.
What’s also important is that students discuss and justify their prediction. It’s not enough to just predict, but they also need to explain why they chose that prediction. Having them reason through their predictions is crucial to the model building process regardless of the accuracy of their predictions or reasoning.
Students will want to use words like “static” and “charge.” I avoided confirming or denying their ideas and instead asked them “what’s charge?” or “what about your observations lead to you talk about charge?” Typically, responses would be “well, like charges repel and opposites attract!”, which describes something well enough, but is likely no more than memorized procedural knowledge. Asking “so, then, what is charge?” a few times usually illustrates the idea I want to get across: charge is more than a few memorized facts.
The experiments they’ve conducted thus far is not enough for students to have constructed a substantial model for electrostatic charge. To follow up, I plan on using these Rutgers Physics Education Group video experiments. The tape activity only showed them like charges and only repelling, nothing else. Part of the goal of the video experiments is to expand upon that.
I will follow the same basic outline: observe, predict. describe. Ideally, students will abstract “peeling tape off of tape” and “rubbing both rods in the same way” to “doing the same thing to two objects” which yields like charges on those objects, which yields similar results. Hopefully, they will extend that and either accurately predict the third video experiment (one rod is positively charged, the other negatively) OR the result will easily “click” with them.This will connect their experience in the lab with previous procedural knowledge of “like charges repel, different charges attract.”
Students will also notice that the tapes, regardless of which one, want to cling to their hands, the table, or anything that isn’t the other piece of tape. They will proclaim that the attraction is due to both objects being oppositely charged, which shows that they don’t yet understand that a charged object can attract a neutral object. Handling that alternative conception, however, is for another day.
After the video experiments, I will be asking students to write down rules for figuring out if two charged objects will attract or repel after watching how they were charged.
How Can I Make it Better?
The most effective improvement I can make is to integrate an extension to this activity that has students performing some procedure that yields tapes with opposite charges. The differences between what they did to tapes that were like-charged and -unlike-charged would need to be clear and easily observable.
I also need to find a way to have students have a more permanent record of their observations. Something as simple as a handout would work. I realized the importance of this halfway through today, and I’m handling it by writing up something myself based on the most common student responses.
There are likely plenty of other ways to make this better. I just haven’t thought of ’em yet! If you’ve got any ideas, please feel free to share!