110 DRIVING SYSTEMS 



The electric charge, in coulombs, produced by a deformation is 



q = K2X 6.45 



where K^ = constant of the crystal, and 



X = deformation, in centimeters at the end of the lever arm. 



The constants Ki and K2 depend upon the dimensions of the crystal 

 and the temperature. It is customary to specify the open circuit voltage 

 as a function of the twist in radians and the twist in radians for the appli- 

 cation of, say, a 60 cycle electromotive force. 



The current generated due to motion is 



i = -7 = K2X 6.46 



at 



The force, in dynes, required to produce a given deformation Is 



/m = xs 6.47 



where s = stiffness of the crystal, in dynes per centimeter. 

 From equations 6.47 and 6.44 the force, in dynes, is 



/m = sKie 6.48 



From equations 6.46 and 6.48 



e 1 /m 



i sKiKo X 



6.49 



where Zem = motional impedance, in ohms, and 



zmt = total mechanical impedance including the crystal with refer- 

 ence to some point of the system. In this example the 

 reference point is at the end of the lever arm. 

 Equation 6.50 is similar to equation 6.43 for the condenser driving sys- 

 tem. The capacity of crystal elements runs from .0002 to .02 mfd. 



Crystal driving elements have been employed for loud speakers, telephone 

 receivers, recording galvanometers, phonograph pickups and recording 

 voltmeters. 



