248 THE BIOPHYSICAL PROBLEM OF NERVE CONDUCTION 



The electric force acting on the electron to depress it is 



2v x 2 y 



Ee = ma 



m 



x 



then 





mi), 



-v 



Fig. VI-21. The path of the electron e entering the idealized uniform electric 

 field between a pair of deflection plates is parabolic. Upon leaving the field the 

 electron moves in a straight line towards the screen Y. 



After leaving the field, the electron travels with speed equal to v at an 

 angle with the axis of the tube until it arrives at the screen, such that 



dy Eex 

 tan = — = o 



dx 



my. 



From the dimensions of the tube 



Equating we have 



tan = 



Eex 



raw, 



Y-y 

 D 



Y-y 

 D 



If D is made large in comparison with half the length of the deflection 

 plate, then 



Tr V e xD 



Y = -j 2 



a m v x 



where E = V/d. The sensitivity is the deflection of the fluorescent spot 

 in centimeters per volt difference of potential applied to the deflection 

 plates; thus 



lex 

 Sensitivity = - • — • —§ • D 

 d m v x 



