ELECTROSTATICS 



25 



sphere to the earth as shown and a positive charge Q = -r ap- 



4 7T 



pears on A and an equal negative charge on the earth. 



Without changing the distribution of flux in any way the nega- 

 tive charge on the earth may be assumed to be collected on a 

 sphere B similar to A but placed at a distance H cm. below the 

 surface. The distribution of potential between two such spheres 

 was worked out in Art. 18. The potential midway between them 

 is zero, the potential at the surface of A is 



Q 



F- Q 

 JJJ ~R~2H-R 



by equation 16, 



and therefore the capacity of the sphere is 



Q i 



c- Q - 



~E~Q 



Q 



1 



electrostatic units. (48) 



R 2H-R R 2H-R 

 When H is very large compared to R the capacity is 



- 

 l/R 



R as in Art. 19. 



+ E 



-Q 2 



Cs 



FIG. 20. Capacities in multiple. 



22. Condensers in Multiple. If a number of condensers of 

 capacities Ci, C 2 and C 3 are connected in multiple, as shown in 

 Fig. 20, and a difference of potential E is applied to the terminals, 



