Appendix C 



Electrical Terminology (Used in Chapters 4 

 through 7) 



There are a number of electrical terms which are used in the discussion 

 of nerve action. The more important ones are included in Table I 

 on page 606. This appendix is devoted to a discussion of some of these 

 quantities and their units. 



The concept of electrical charge is hard to define. The unit of charge 

 may be defined in terms of Coulomb's law giving the force of interaction 

 between two charges separated by a distance r; that is 



F M* 



Kr 2 



If K is given the appropriate value for mks units, namely ^ttcq, 1 and F is 

 in newtons and r in meters, the ^'s will be in coulombs. The force will 

 be repulsive if the two charges have the same sign and attractive if the 

 signs are opposite. 



Because there exist forces between charges, it will in general require 

 work to bring a new charge into any region of space. The work neces- 

 sary to move a unit charge between two points is called the potential 

 difference V. Symbolically, this is expressed as 



dq 

 If a potential difference exists between two points, there will be a 



1 The symbol e stands for the dielectric constant of free space. 



605 



