FL UCTUA TIONS IN MICROPHONES AND O THER RESIST A NCES 2 1 \ 



o 



z 



|CMO 



" V 



(>—»«- 



(1 >. 



500 1000 



FREQUENCY IN CYCLES PER SECOND 



Fig. 11— The frequency distribution of the contact noise in a 50,000-ohm carbon 

 grid leak resistor. The method of plotting the experimental points is the same as 

 that shown in Fig. 10. 



as yet, to obtain dependable results. For a satisfactory observation of 

 the effect of temperature on the noise of contacts one must be certain 

 that the conducting area in a contact remains constant and inde- 

 pendent of temperature. Temperature variations can alter the con- 

 ducting area in at least two ways; the contacting particles may be 

 relatively displaced due to differential thermal expansions of the 

 apparatus, and the change of the quantity of adsorbed gas on the 

 contacting surfaces can alter the contacting areas without any relative 

 displacement of the contacting particles. Both of these conditions are 

 very difficult to control in any measurement involving temperature 

 changes. However, our measurements of the relationship between 

 contact noise and temperature, performed under the most carefully 

 controlled conditions which we have been able to apply, indicate that 

 contact noise may change either positively or negatively as a function 



