Notes

Many Physics courses include a unit on Static Electricity. And a common topic in such a unit is the manner in which objects become charged. One such method is the method commonly referred to as charging by induction. The induction charging process can be thought of as occurring in two steps. In the first step, a charged object is brought near to a neutral conducting object. The presence of the charged object near the neutral conductor induces a movement of electrons within the conductor. They are drawn towards a positively-charged inducer and pushed away from a negatively-charged inducer. This causes a polarization of the neutral object. When the neutral object is then touched by a ground (finger, a second object, etc), there is a transfer of electrons between the neutral object and the ground. When the ground is pulled away, the once neutral conductor is now left with a permanent charge. The charge it acquires is opposite that of the inducer.

The method of charging by induction can be easily demonstrated and experimented with using low-cost equipment. Pie tins, styrofoam plates, balloons, samples of wool clothing, or a good batch of head hair is typically all that is needed to do such demonstrations or to provide such lab experiences. This Concept Builder (or any of our Concept Builder) is not intended to replace such a hands-on experience; rather it is intended to support such experiences. The activity gets students thinking about the invisible - the movement of particles. The method of charging by induction and this Concept Builder provide a support for a common theme in science - the macroscopic world that we see can be explained in terms of particles that cannot be seen.

We recommend that the hands-on activities and demonstrations be presented in advance of doing this Concept Builder. We think it works best near the middle to end of a learning cycle on charging methods. There are three levels of difficulty in this Concept Builder. Each level includes four different questions. Unlike many of our Concept Builders, there is no question grouping. So every student will get the same set of questions. The order of presentation will be different and the answer options will be scrambled for each student such that the eight answer options are displayed in a different order for different students. Questions within the various difficulty levels can be distinguished from each other as follows:
 

• Apprentice Difficulty Level: Question Groups 1-4. In each case, a charged object is brought near a neutral object. Then the neutral object is touched by a finger.
• Master Difficulty Level: Question Groups 5-8. In each case, a charged object is brought near a neutral object. Then the neutral object is touched by a second neutral object.
• Wizard Difficulty Level: Question Groups 1-8. Includes every question from the first two difficulty levels.

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 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 Charging by Induction Concept Builder. These include:
 

Additional resources and ideas for incorporating this Charging by Induction 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.