82 THK BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1954 



Fig. 2 — Magnetic parts, coil, and actuating card of AJ relay. 



netization curves. The clashed curve of Fig. 1 is the decreasing magneti- 

 zation curve for the same gap as the adjacent magnetization curve. 



([/ is a function of x, and changes as the armature moves. If this 

 motion occurs at a constant value of (p, there is no induced voltage and 

 hence no electrical transfer of energy. A decrease in U must therefore 

 represent mechanical work done on the armature. For a differential 

 change dx in armature position, the mechanical work is Fdx, where F is 

 the pull exerted on the armature. A general expression for F is therefore 

 given by: 



F = 



dU 



dx (^ constant) 



(2) 



