Many Physics courses include a unit on Static Electricity. And perhaps the most commonly introduced topic in such a unit is the topic of charge interactions. Students must know and be able to use the concepts of how two charges interact in order to identify the charge on an object. It is a crucial skill to have when conducting experimental studies in Static Electricity. Students must understand and have a comfort with using the ideas that oppositely charged objects attract each other, like-charged objects repel each other, and charged and neutral objects attract each other.

Inclusion of the topic of charge interactions into the curriculum provides a great opportiunity to challenge students with exercises that require the implementation of logical reasoning in order to determine the type of charge on an object when the objects interaction with other objects is observed. This Concept Builder (and a related one titled Charge Interactions) majors on this as it provides students with a description of the interactions between two to three balloons (and on occassion, between one of the balloons and some neutral bits of paper) and then ask students to reason towards what the charge on one of the balloons. The activity is a great example of simple rules regarding charge interactions being used with higher order thinking skills.

As mentioned, this is our second Concept Builder that details this skill. Our first Concept Builder which we created on this concept - Charge Interactions - ended up being too difficult for many students. And at times a "too difficult" Concept Builder becomes a exercise in frustration rather than an exercise in learning. We believe that Getting the Hang of Charge is considerably more manageable and should be undertaken before our Charge Interactions Concept Builder. We actually recommend starting with the Apprentice Difficulty Level of Getting the Hang of Charge and continuing as far as a teacher feels their students can manage. For many Honors, AP1, and IB Physics classes, the Charge Interactions Concept Builder will be a natural next step. 

There are three different difficulty levels that can be engaged in through the Concept Builder. Those three levels are differentiated as follows:
 

• Apprentice Difficulty Level: Question Groups 1-4. Interactions between Balloon A of known charge and Balloon B of unknown charge are described and depicted. The charge on Balloon B must be determined.
• Master Difficulty Level: Question Groups 5-12. Interactions between Balloon A (of known charge) and Balloon B and between Balloon B and Balloon C are desribed and depicted. On occassion, the interaction of Balloon B or C with paper bits is also described. The charge on either Balloon B or Balloon C must be determined.
• Wizard Difficulty Level: Question Groups 13-16. Interactions between Balloon A (of known charge) and Balloon B and between Balloon B and Balloon C are desribed and depicted. The interaction of Balloon B or C with paper bits is also described. The charge on either Balloon B or Balloon C must be determined. There are usually multiple possible answers.

To gain a feel for the cognitive difficulty of this Concept Builder, we recommend that teachers attempt to complete one of the difficulty levels. Alternatively, the questions are provided in a separate file for preview purposes. We can imagine it being profitable to allow students to make judgements as to what level to begin with and to progress from easier to more difficult levels. Questions in the various levels are unique to that level and are not seen in other levels.

In order to complete a level, a student must correctly analyze each question at that level. If a student's analysis is incorrect, then the student will have to correctly analyze the same or very similar question twice in order to successfully complete the level. This approach provides the student extra practice on questions for which they exhibited difficulty. As a student progresses through a level, a system of stars and other indicators are used to indicate progress on the level. A star is an indicator of correctly analyzing the question. Once a star is earned, that question is removed from the queue of questions to be analyzed. Each situation is color-coded with either a yellow or a red box. A red box indicates that the student has incorrectly analyzed the question and will have to correctly analyze it twice before earning a star. A yellow box is an indicator that the question must be correctly analyzed one time in order to earn a star. Once every question at a level has been analyzed, the student earns a Trophy which is displayed on the Main Menu. This system of stars and trophies allows a teacher to easily check-off student progress or offer credit for completing assigned levels.

The most valuable (and most overlooked) aspect of this Concept Builder is the Help Me! feature. Each question group is accompanied by a Help page that discusses the specifics of the question. This Help feature transforms the activity from a question-answering activity into a concept-building activity. The student who takes the time to use the Help pages can be transformed from a guesser to a learner and from an unsure student to a confident student. The "meat and potatoes" of the Help pages are in the sections titled "How to Think About This Situation:" Students need to be encouraged by teachers to use the Help Me! button and to read this section of the page. A student that takes time to reflect upon how they are answering the question and how an expert would think about the situation can transform their naivete into expertise. 

 

 

There are numerous resources at The Physics Classroom website that serve as very complementary supports for the Charge Interactions Concept Builder. These include:
 

 

 

Additional resources and ideas for incorporating this Charge Interactions Concept Builder into an instructional unit on Static Electricity can be found at the Teacher Toolkits section of The Physics Classroom website.  Visit Teacher Toolkits.