PROBLEMS. 387 



32. A circuit has an inductance of 0.2 henry and a resistance 

 of 6 ohms. Calculate the effective value of the current produced 

 by an electromotive force of which the effective value is 100 volts 

 and of which the frequency is 60 cycles per second. Calculate 

 the phase difference between electromotive force and current. 

 Ans. Current 1.32 amperes, phase difference 85 27'. 



33. (a) Calculate the reactance value of o. 1 2 henry at 60 cycles 

 per second. (^) Calculate the reactance value of a 20 micro- 

 farad condenser at 60 cycles per second, (c) Calculate the 

 reactance of both in series, (d) At what frequency is the react- 

 ance value of both in series equal to zero? Ans. (a) ,45.2 ohms, 

 (&) 132.6 ohms, (c) 87.39 ohms, (d) 102.7 cycles per second. 



34. A harmonic electromotive force of 1,100 volts (effective) 

 produces a harmonic current of 100 amperes (effective) in a given 

 circuit, the current being 20 behind the electromotive force in 

 phase. Calculate the resistance, reactance, and impedance of the 

 circuit. Ans. Resistance 10.34 ohms, reactance 3.76 ohms, 

 impedance 1 1 ohms. 



35. A harmonic electromotive force of 1 1 o volts produces a 

 current of 1 5 amperes in a receiving circuit of which the power 

 factor is equal to 0.7. Find the values of resistance, reactance, 

 and impedance. Ans. Resistance 5.13 ohms, reactance 5.24 

 ohms, impedance 7.33 ohms. 



Note. From the data of this problem it is impossible to determine whether the 

 current is ahead of or behind the electromotive force in phase. It is desirable always 

 in specifying the value of a power factor of a receiving circuit to state whether the cur- 

 rent leads or lags ; thus one would speak of a 70 per cent, leading power factor or a 

 70 per cent, lagging power factor, as the case may be. 



36. Alternating-current mains deliver 100 amperes of current 

 to a non-inductive circuit, to glow lamps for example. An in- 

 ductive circuit of negligible resistance is then connected to the 

 mains and it takes 10 amperes. What is the total current deliv- 

 ered by the mains? Ans. 100.5 amperes. 



37. From the data of problem 34, find the conductance, sus- 

 ceptance and admittance of the circuit. Ans. (a) 0.0854 recipro- 



