46 STATIC ELECTRICITY 



since no work is done in carrying the unit from point to point. 

 It is, therefore, the same as the value at O. As all UK- di 

 is at the same distance from O, 



r OA 7 



The same result is obtained by putting the potential of the spl 

 equal to the value at A, which is obtained by supposing H to n 

 up to A, whence 



The. energy of the charge, since it is all at the same- poU-ntinl, i- 







