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.