198 TREATISE ON ALTERNATING CURRENTS. 



18. What capacity must be placed in (1) parallel, and (2) in series with 

 the arrangement in question 17 to produce resonance ? 



Answers. (1) 3134 microfarads ; (2) 3184 microfarads. 



19. Two circuits of 100 ohms and O'l henry self-induction, and 50 ohms and 

 20 microfarads respectively, are connected (1) in series and (2) in parallel. 

 Find the total currents, and also the difference of phase between the P.D. and 

 current in the two cases, the P.D. being 1000 volts, and the frequency 50 periods 

 per second. 



Answers. (1) 5-076 amperes, 40 20' lead. 



(2) 11-26 amperes, 14 40' lead. 



20. An induction motor takes 75 amperes on full load, when its power factor 

 is 0'83 : what is (1) the energy current, and (2) the wattless current? 



Answers. Energy current = 62*25 amperes. 



Wattless current = 41-85 amperes. 



21. What capacity placed in parallel with the induction motor in Question 20 

 will make the power factor 0-9 on a 500- volt 50 frequency circuit ? 



Answer. 74*44 microfarads, nearly. 



22. What capacity placed in parallel with the induction motor in Question 21 

 will make the power factor unity if the frequency is 100 cycles per second ? 



Ansiver. 133-2 microfarads, nearly. 



