ELECTROSTATICS 15 



The charge q on B produces at P an electrostatic force 



9/y 



dynes, 



D-r 



in the same direction as & A . 

 The resultant force at P is 



dynes. . . . (22) 



Curve ( 1) , e = 2 q log 

 Curve (2) 



FIG. 12. Potential and potential gradient between two parallel wires. 



The potential at the point midway between the two wires is 

 zero and therefore the potential at the point P is 



2?[logr-log(Z)-r)]f /2 

 D-r 



This equation is plotted in curve 1, Fig. 12. 

 The potential at wire A is 



D-R 



(23) 



(24) 



