CHAPTER VI 



ELECTRICAL LEVEL OR POTENTIAL. THE 

 ENERGY IN ELECTRIFIED SYSTEMS 



Electrical level Potential at a point Equipotential surfaces Intensity 

 expressed in terms of rate of change of potential General nature of 

 level surf ices Energy of an electrified system in terras of charges and 

 potentials Unit cells Number of unit cells in a system double the 

 number of units of energy Distribution of energy in a system. 



THE existence of forces on charged bodies in an elerhilu.i 

 implies that these bodies may be set in motion, or that the sy> 

 contains energy which may appear in the kinetic form. \NY must 

 suppose that before its appearance as kinetic energy, it was stored 

 in some way as electric energy,and in that form was the equivalent 

 of the work done in charging the system, Regarding the s\- 

 from this " work " point of view, we are led to the idea of elert i 

 level or potential, which affords meet valuable aid in dex-rihing the 

 system in respect to the forces exerted and to the energy stored. 

 We have already discussed the potential in invi TM- Mjtiare systems 

 in Chapter III, but we shall now approach the subject from another 

 point of view. 



Electrical level. If a positively charged conduct* 

 suspended in the middle of a room a small body brought again-t it 

 will receive a little of the charge and will thru tend to move to the 

 wall, on which is the negative charge. Let us imagine that the 

 small carrier has no weight so that we need not think of any but 

 the electric forces. At the wall we may think of it as going into 

 a hole and touching the side of the hole, when it will be entirely 

 discharged. It can then be moved back to the large body, where 

 it will receive a little more charge, go again to the wall, and so on. 

 On each journey from the body to the wall it can be made to do 

 work, and the system will gradually yield up its energy. Now 

 compare this with what happens in a system containing gravitative 

 energy, such as a reservoir of water on a high level. We may let 

 the water run down to a lower level and gradually transform the 

 potential energy into some other form in the process. Or, to make 

 the cases more alike, we may let the water down by a bucket which 

 corresponds to the electrical carrier. The water gives up its energy 

 by falling in level. 



Using this analogy, we may describe the electrified body in the 



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