IMPEDANCE. 



Hence from the triangle cos (f> = 



sin <f> 



10 



OR 



OR 

 RI 



S 



' + (2 



The impedance of a circuit or part of a circuit is of very 

 great importance, and the following experiments illustrate 

 the various factors upon which the impedance depends. 



As a practical and convenient example, an ordinary arc 

 lamp choking coil may be taken for the purpose of the 

 following measurements. The methods may, however, 

 equally well be applied to any other form of inductive 

 resistance, e.g., an armature coil of an alternator, magnet 

 winding, &c. 



The three variable quantities in the expression 



V R* + (2 TT n LY for the impedance are : (1) The resistance, R ; 

 (2) the periodicity, n ; (3) the self-induction L. 



In order to determine the influence of each variable 

 separately, two of them must be kept constant, while the 

 third is varied. 



EXPERIMENT III. DETERMINATION OF DEPENDENCE OF 

 IMPEDANCE UPON RESISTANCE. 



If the coil on which the measurement is made contains 

 iron, variation in current will produce variations in the 

 permeability of the iron, and consequently variations in 

 the self-induction of the circuit. 



Therefore it is necessary in this experiment to maintain 

 the current approximately constant. 



DIAGRAM OF CONNECTIONS. 



FIG. 16. 



