IMPEDANCE. 



45 



as its magnetic saturation is altered. Consequently the 

 permeability of the iron will depend upon the strength of 

 the current producing the field, and the self-induction of 

 the coil will have a different value for each value of the 

 current. 



Obviously there will actually be a constant and rapid 

 change in the permeability of the iron corresponding to the 

 changing value of the alternating current. It is only the 

 mean value for a given current with which we are at present 

 concerned. 



DIAGRAM OF CONNECTIONS. 

 As for Experiment IV. page 39. 



Instructions. Connect in series with a supply of alter- 

 nating current a variable resistance, the inductive coil to be 

 experimented upon, and an ammeter. Connect a voltmeter 

 to the terminals of the inductive coil. 



By means of the resistance E vary the current in the 

 circuit from a low value upwards. The frequency must be 

 maintained constant. For each value of the current read 

 ammeter and voltmeter, and tabulate the reading as follows : 



DETERMINATION OF IMPEDANCE AT VARIOUS CURRENTS. 

 Coil No Frequency of Current 37 



The readings should also be recorded in the form of a 

 curve, as in Fig. 21, the 'current being plotted horizontally, 

 and the impedance vertically. 



The results shown in the upper curve Fig. 21 were obtained 

 on the choking coil already experimented upon with currents 

 having a periodicity of 37. 



