38 ELEMENTS OF ELECTRICITY AND MAGNETISM. 



Definition of the volt on the basis of O Jim's Law. According 

 to equation (7^), the electromotive force required to force a cur- 

 rent through a circuit is equal to the product of the resistance 

 of the circuit and the current. When the resistance is expressed 

 in ohms and the current in amperes, this equation gives the value 

 of the electromotive force in volts. That is to say, a voltaic 

 cell, or any electric generator (assumed, for the sake of simplicity 

 of statement to have no internal resistance and to be unaffected 

 by those secondary influences which cause a decrease of electro- 

 motive force with delivery of current), has an electromotive force 

 of one volt if it produces one ampere of current in a circuit of 

 which the resistance is one ohm. 



20. Application of equations (2), (6) and (7) to a portion of an 

 electrical circuit. Equation (2) expresses the heat which is 

 generated in a portion of the electrical circuit, R being the 

 resistance of that portion. Equation (6) expresses the power 

 which is delivered to a portion of an electrical circuit, E being 

 the electromotive force across the terminals of that portion. 

 Equation (7) expresses the relationship between the current in an 

 electrical circuit, the electromotive force across any given portion 

 of the circuit, and the resistance of that portion. 



The current produced by a voltaic cell not only flows through 

 the wire which is connected to the terminals of the cell, but it 

 flows also through the electrolyte in the cell. Let EJ repre- 

 sent the total rate at which work is supplied by the voltaic cell 

 in the maintenance of the current, let R x be the resistance of the 

 external circuit of wire, and let R a be the resistance of the 

 electrolyte and electrodes in the cell. Then the rate at which 

 heat is generated in the entire circuit is (R a + R x )f 2 , and this is 



equal to El, so that 



%-RJ+RJ 



whence 



RJ=E t -RJ (8) 



but RJ is the electromotive force which is required to force the 

 current / through the external resistance R x ; that is, RJ is 



