SPACE CHARGE BETWEEN PARALLEL PLANE ELECTRODES 57 



It should be noted that while some of the curves in the D region 

 shown in Fig. 3 resemble the portions of the curves drawn in light 

 lines on Fig. 2, the curves in Fig. 3 have essentially different physical 

 content, representing solutions in which all of the injected current is 

 transmitted. Values of a and ip may, therefore, be entered in all 

 regions on Fig. 3 while entering values on Fig. 2 are restricted to the 

 regions covered by the heavy lines. 



The occurrence of overlap regions indicates that for certain boundary 

 conditions more than one type of potential distribution may exist. 

 In the practical case the choice between these various possible solu- 

 tions depends upon the manner in which the boundary conditions are 

 established.^^ 



Current Injection from Both Sides 



The present analysis although derived on the assumption of current 

 injection from one side only is equally applicable to the situation 

 shown schematically in Fig. 5. The potential distribution curves 



I 



•PaVa 



OR (pt)Vt, 



Vb 



-CTaS. 



a^a- 



cfb^b" 



lb 



PLANE 



a 



PLANE 



b 



Fig. 5 — Schematic representation of the general conditions under which the potential 

 distribution analysis may be applied. 



which occur when the currents /„ and /& are injected from opposite 

 sides will be identical with those obtained for an assumed injection 

 from one side only of a current / equal to the numerical sum of /„ and 

 /ft. Values of V\, <p and o- are chosen to correspond with an assumed 

 direction of injection and these values are entered on the figures. 

 For solutions of the B type, different distributions will result depending 



'^ This matter will be treated in more detail in the section on circuit charac- 

 teristics. 



