Method of Measuring Energy dissipated in Condensers. 27 



there is complete resonance. The two parallel circuits having 

 the same impedance take the same current ; one current is 

 nearly 90° ahead in phase of the electromotive force (see 



Fig. 5. 



N 



W-M 



Condenser 



Dyn. 



Coi? 



curve 2, fig. 6), the other is nearly 90° behind (curve 3), the 

 sum of the two being relatively very small (curve 4) and in 

 phase with the impressed electromotive force (curve 1). The 

 shunt resistance must be applied at the high voltage terminals, 

 but as a small amount of self-induction produces no appre- 

 ciable error in the wattmeter, the movable coil may be long- 

 enough to make the wattmeter quite sensitive, and so a quite 

 small shunt current may be used. This requires a larger 

 resistance, but with much smaller carrying capacity, since a 

 much smaller shunt current will suffice than when the main 

 current differs largely in phase from the shunt current. 



To illustrate this point, suppose as before that for a given 

 condenser the angle of advance of the current is 89° 40'. 

 The power factor, cos <j>, in the expression watts = E I cos <£ 

 is in this case '00582. If now a resonance-coil be placed in 

 parallel with the condenser and the current in the fixed coil 

 of the wattmeter brought into phase with the electromotive 

 force, then cos <£ = 1. To get a certain deflexion of the watt- 

 meter, therefore, we must have the product of the two currents 

 in the wattmeter nearly 200 times as great in the first case 



