THE CARBON MICROPHONE 



185 



ment and resistance-force characteristics and if F, D and R be the 

 contact force, the contact displacement and the contact resistance, 



DISPLACEMENT IN CENTIMETERS X 10" 



Fig. 20 — Typical force-displacement characteristics of carbon granules pressed 

 against a polished carbon plate. 



respectively, we may express our results by the approximate relations: 



F = const. -i)^", 

 R = const. -T^-^. 



(1) 

 (2) 



The values N" and N are not, however, independent of the force or 

 displacement limits when these limits are relatively small. In Fig. 22 

 we have plotted values of N" and N as functions of the difference 

 between the maximum and minimum displacement (AD). We see 

 that for relatively large values of AD, N" and N approach the limiting 

 values 3.1 and 0.47, respectively, but for smaller values of AD, N" 



