14 



ELECTROMOTIVE FORCE AND CURRENT. 



Consequently a curve showing rate of change of current 

 per second would be a curve similar to curve II., but having 

 each ordinate n times its value. 



Since the electromotive force of self-induction is propor- 

 tional to the rate of change of lines caused by the current, and 



FIG. 6.-CURVES OF CURRENT AND RATE OF CHANGE OF CURRENT. 



since these lines are necessarily proportional to the current 

 itself, curve I. will show the manner in which the number of 

 lines in the circuit fluctuates, and curve II. will represent 

 the variations undergone by the electromotive force. 



The actual value of this electromotive force must now be 

 investigated. 



Coefficient of Self-induction. Let c = value of current in 

 the coil at any moment. 



N = number of turns composing the coil. 

 Z = number of lines of force produced in the coil 

 when c = 1 ampere. 



Then, when the current changes at the rate of 1 ampere 

 per second, the change produced in the number of lines 



