4 ELECTRICAL ENGINEERING 



This density is produced over the surface of a sphere of radius r 

 and therefore the total dielectric flux from the charge q is 



\I/ = \ X 4 irr 2 = 4 jrq lines. 



Consider the same charge surrounded by a medium of dielectric 

 constant K. 



The force exerted on a unit charge at a distance r cm. from 

 q is 



the dielectric flux density produced is 



3) = &K = z lines per square centimeter, 



and therefore the dielectric flux from charge q is, as before, 



^ = 4 Trq lines. . ...... (4) 



Fig. 1 represents the electrostatic field about a positive point 

 charge. The lines of flux extend out radially in all directions. 



FIG. 1. Field surrounding a point charge. 



8. Dielectric Flux from a Unit Charge. The dielectric flux 

 from a unit charge is 4 TT lines by equation 4. Thus if a dielectric 

 flux \j/ starts from any surface the positive charge on that surface 



is q = -p- units, and if a flux ^ ends on any surface the negative 



r 7T 



charge on that surface is q = - units. 



