U2 SINGLE-PHASE CURRENTS. [Exp. 



the coil; and third, for the resistance and coil combined. Vary 

 the current, by means of the adjusting resistance, and take several 

 sets of readings, the current being kept constant for each set; 

 see 24a. 



30. The ammeter and current coil of the wattmeter are in 

 series with the circuit for all readings and their location is un- 

 changed. The voltmeter and the voltage coil of the wattmeter 

 are in parallel with each other and are connected : first, across the 

 terminals of the resistance; second, across the terminals of the 

 coil; and third, across the terminals of the resistance and coil 

 combined. These changes can be most readily made by means of 

 a voltmeter switch, the current being maintained constant during 

 one set of readings by means of the adjusting resistance. Some 

 error is here introduced on account of the power consumed in the 

 instruments. 



31. Repeat at a second frequency. 



32. (d) Resistance and Coil in Parallel. Connect the resist- 

 ance R-L and the coil R 2 L 2 in parallel, and, together with the 

 adjusting resistance, connect to the supply as in Fig. 10. For 

 a certain constant voltage E, take readings of current, voltage 

 and watts: first, for the resistance alone; second, for the 

 coil alone; and third, for the resistance and coil together in 

 parallel. 



Vary the voltage by means of the adjusting resistance, and take 

 several sets of readings, the voltage being kept constant for each 

 set ; see 24a. 



33. The voltmeter and potential coil of the wattmeter are not 

 changed during the readings. The ammeter and the current coil 

 of the wattmeter are shifted from one circuit to another, being: 

 first, in series with the resistance ; second, in series with the coil ; 

 and third, in the main circuit. Since, during one set of readings, 

 the voltage is maintained constant, the readings thus obtained* 



* This would be true if the instruments themselves took no power; 

 233. 



