16 ELECTRICAL ENGINEERING 



and that at B is 



(25) 



The difference of potential between the two wires is 



E = E A -E B = q\og2^ ..... (26) 

 E can also be obtained as 



/ & dr = 4 q log 

 JR 



D-R 

 R 



The potential gradient between A and B, which is equal to 

 the intensity of the electrostatic field, is given by equation 



plotted as curve 2, Fig. 12. 



At the surface of the wires its value is maximum. 



Midway between the wires its value is minimum. 



0min. =: ~ri 



If the two wires are suspended in a medium of dielectric con- 

 stant K, the distribution of flux is not changed but the intensity 

 of the electrostatic field and therefore the potential gradient and 

 potential at each point are reduced in the ratio l/K, and the 

 difference of potential between the wires becomes 



*-7? lo8 T ....... (30) 



19. Capacity. Conductors of different sizes and shapes have 

 different capacities for storing electricity. If two conductors of 

 different capacities are charged with equal quantities of electricity, 

 they will be raised to different potentials, the one of small capacity 

 will be raised to a high potential and the one of large capacity to 

 a low potential. 



