Summary
- There are two kinds of charge, positive and negative.
- Like charges repel; unlike charges attract.
- There are two main classes of materials. These are insulators, in which the charge is essentially fixed in place, and conductors, in which the charge is free to move. There is also a useful intermediate class called semi-conductors in which the conducting properties can be adjusted by adding impurities.
- When one insulator is rubbed on another, which one ends up positive and which ends up negative is determined by their location in the triboelectric series.
- The electroscope can be used to tell the difference between a positively charged object and a negatively charged object.