176 HOW WE PRODUCE ELECTRICITY 



Charged Bodies. In this experiment we learned that 

 when a hard rubber rod is rubbed with fur, the rod repels 

 a rubber balloon which had previously been rubbed with 

 fur. But a glass rod rubbed with silk attracted the 

 balloon. Evidently there are two kinds of electric 

 charges. According to our present theory of matter, 

 each neutral atom is composed of a positive nucleus or 

 central portion. The particles which make it positive 

 are called protons. Negative particles of electricity 

 called electrons are believed to revolve around the nucleus. 

 The atom is normally made up of equal numbers of protons 



and electrons, the former 

 being entirely inside the 

 nucleus . There is a strong 

 attraction between the 

 protons in the nucleus 

 and the electrons, but 

 some of the electrons can 

 be separated from the 



Where did the electrons shown on the silk outer t of the atom 



come from? 



Protons never leave the 



atom to go into another body. When we rubbed the glass 

 and silk together, some of the electrons were transferred 

 from the glass to the silk. This makes the silk negative. 

 The glass rubbed with silk having lost electrons now has 

 more protons than electrons and so it is positively electri- 

 fied. When hard rubber is rubbed with fur, electrons go 

 from the fur into the hard rubber, making the fur posi- 

 tively electrified and the hard rubber negatively electrified. 

 Whenever electrification is produced by friction between 

 two bodies, the positive charge produced in one equals in 

 amount the negative produced in the other. It was Ben- 

 jamin Franklin who first suggested the names positive and 

 negative for these two kinds of electrification. From 

 these experiments we can make the general statement 



