30 



ELECTROMOTIVE FORCE AND CURRENT. 



MI, M.,. Source of alternating current. 



r. Resistance partly inductive and partly non- 

 inductive.* 



R. Non-inductive resistance. 

 F x . Voltmeter reading voltage of inductive 



resistance r. 

 V.,. Voltmeter reading voltage of non-inductive 



resistance R. 



V s . Voltmeter reading total voltage of R + r. 

 A. Ammeter. 



Instructions. The portion of the circuit in which the 

 angle of lag is to be determined will consist partly of inductive 

 and partly non-inductive resistances ; this is represented by r 

 in the diagram. 



Insert in the circuit a non-inductive resistance, R, and an 

 ammeter. 



Connect three voltmeters^ to points in the circuit so as 

 to measure respectively (1) the voltage at terminals of non- 

 inductive resistance (F 2 ), (2) voltage of r (VJ, (3) total 

 voltage of circuit (F 3 ). 



Take simultaneous readings on the ammeter and three 

 voltmeters, and enter them in columns headed as given 

 below : 



The readings should, if possible, be repeated for several 

 values of the current, obtained by altering the voltage of 

 supply or by a resistance in series with R and r. 



The angle of lag of the circuit must then be determined 

 for each set of readings by construction similar to that 

 described in the previous experiment. 



Draw a horizontal line to represent to a convenient scale 

 the total voltage of the circuit. Draw from opposite ends 



* All so-called " inductive resistances " are partly non-inductive, since 

 they necessarily have some ohmic resistance. 



t A single voltmeter and multiple-way switch may be used instead of the 

 three voltmeters, 



