CHAPTER XV 



INTERACTIONS OF MOVING ELECTRONS IN CON- 

 DUCTING CIRCUITS 



WHEN two electrons tractate, the space rate at which 

 their potential energy varies is given by Coulomb's 

 Law. This law, however, holds only for electrons 

 which are at rest, for even it the separation is constant 

 the potential energy of the system will be constant 

 only if its parts are not hi motion. This phenomenon 

 is the basis of those so-called electro-magnetic methods 

 for converting mechanical energy and electrical energy 

 which are utilized by the ''electrical power" industry. 



The reasoning which we shall follow hi discussing 

 this behavior of electrons may be illustrated by con- 

 sidering a somewhat similar problem of mechanics. 

 A body resting on the surface of the earth is revolving 

 about the terrestrial axis much like a bit of mud on an 

 automobile tire. The tendency of the mud to fly off 

 at a tangent is merely another instance of the inertia 

 which Newton recognized. The greater the kinetic 

 energy of the mud, the more pronounced is this tend- 

 ' ency and the greater must be its adhesion to the tire, 

 if it is not to fly off. 



The body has potential energy with the earth and 

 also its own kinetic energy. The latter is divided among 

 two degrees of freedom, one along the line of centers, 



195 



