832 THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1951 



The determining conditions that can be measured in any physical circuit 

 associated with the diode are: the total current, the conduction current at 

 the first plane, and the electron velocity at that plane. Then, for conveniently 

 considering the diode as a circuit element, it has been shown by others^ that 

 we should be able to calculate the conduction current at the second plane, 

 the electron velocity at that plane, and the resultant voltage across the 

 diode. From the viewpoint of circuit theory, these last three quantities may 

 be considered as dependent variables whose solutions should be sought in 

 terms of the initial conditions. But an electron stream flows according to 

 its own nature, with little regard for circuit theory, its fundamental equa- 



CURRENT FLOW 

 ELECTRON MOTION 



PLANE , , PLANE 



[ x-„-> I 



I I 



I I 



I I 



[<_ z J 



Fig. I — Parallel plane diode with a first plane (a) and a second plane (b), 



tions involve electric intensity and electron velocity as the dependent 

 variables, and the general theory must therefore be developed in terms of 

 these naturally occurring quantities. But it should be noted that the desired 

 circuit relations can always be calculated from these fundamental variables. 



1.1 Units and Symbols 



The equations are written in practical electrical units, centimeters, grams 



and seconds. In this system of units, the permittivity € of a vacuum is 



10-^^ 



^— — , and the acceleration constant -n of an electron is approximately 



oox 



1.77 '10*^. To conform with circuit convention, the total current and the 



conduction current are measured in the negative :r-direction, that is, opposite 



to the motion of the electrons; all other directed quantities are measured in 



the positive x-direction. 



