IMPEDANCE. 



41 



impedance ^R 2 + (2nLy was very nearly equal to 

 the reactance 2 TT n L, because the value of R was so small. 

 Evidently the reactance increases in direct proportion to n, 

 the frequency. This is shown to be the case by the straight- 

 ness of the curve, which only bends very slightly at the bottom 

 when the frequency becomes so small that the reactance 

 becomes comparable with the resistance. 



- 2 



10 



40 



50 



20 30 



Frequency. 



PIG. 19. CURVES SHOWING DEPENDENCE OF IMPEDANCK ON FREQUENCY. 

 Lower Curve, Coil alone-. Upper Curve, Coil and Resistance. 



The upper curve shows readings of the impedance of the 

 coil, and a resistance of 1*85 ohms in series taken at the 

 same time. The resistance in this case is much larger compared 

 with the reactance, and the curve is affected much more by 

 the resistance near its lower end. At very high frequencies 

 indeed, the reactance would become so great that the 

 resistance would be negligible, and the two curves would 

 then coincide, since the reactance factor of the impedance is 

 the same for both curves. 



The important point to be learnt from the results of this 

 experiment is that the impedance of any circuit consists of 



