ELECTRICAL ENERGY. 77 



CHAPTER V. 

 WORK OF ELECTRICAL FORCES. 



88. ELECTRICAL ENERGY. When different electrical conductors 

 are connected with the earth, the system reverts to the neutral state, 

 and in doing so performs work which is necessarily positive. Any 

 given system of electrical conductors possesses a store of available 

 energy corresponding to this work ; it is a potential energy, which we 

 may simply speak of as electrical energy. 



The electrification of a system, requires the expenditure of an 

 amount of work equal to the potential energy which it possesses in 

 this new condition. 



When two conductors are connected, a change is in general 

 produced in the distribution of the electrical masses, and this 

 modification corresponds to a positive work. The electrical energy 

 of a system of conductors is therefore equal, or superior, to that 

 of the system obtained by connecting all these conductors in any 

 way whatever. 



When the system contains an electrified insulating body, we may 

 look upon the several electrified masses, with which the body is 

 charged, as belonging to infinitely small conductors. If all the 

 masses are connected together, the energy diminishes. The energy 

 of a system of bodies, each of which possesses a given mass, is 

 therefore a minimum when all the bodies are conductors. 



The potential energy of a system may be measured either by 

 the work expended in electrifying it, or by the work which is per- 

 formed by its discharge. 



89. ENERGY OF A SINGLE CONDUCTOR. Let us first consider 

 a single conductor of capacity C, and let us suppose that a charge 

 M has been given to it, which raises it to potential V. To increase 

 the charge by dM, this quantity */M of electricity must be brought 

 from infinity, or from the earth, to the conductor, and the work 

 expended in this operation is equal to WM. 



