386 ELEMENTS OF ELECTRICAL ENGINEERING. 



would reach if it were to continue changing at this rate for J of 

 a cycle. Ans. (a) 17,725 amperes per second, (ff) 33.3 amperes. 



28. A 60 cycle alternator giving a harmonic electromotive 

 force of which the effective value is 1 10 volts acts upon a circuit 

 of which the inductance is 0.02 henry and of which the resistance 

 is negligible. Find the effective value of the current produced. 

 Ans. 14.6 amperes. 



29. An alternator having a harmonic electromotive force of 140 volts (effective) 

 delivers 200 amperes (effective) to a circuit of which the power factor is 0.70. Find 

 the maximum positive and maximum negative values of ei. Ans. 47,60x3 watts, 

 8,400 watts. 



Note. The algebraic expression for e is <? = E sin ut where E= 1/2 X HO 

 volts, and the algebraic expression for i is i= I sin (ut 0), where 1=: |/2X 2 

 amperes, and 6 is the angle whose cosine is 0.70. Therefore 



ei = El sin ut sin (ut 0), 

 and it is required to find the maximum and minimum values of this function. 



30. (a) Find the power component and the wattless component 

 of the current in the fan motor specified in problem 25, these 

 components being taken with reference to the voltage across the 

 terminals of the motor, (b) Find the power component and 

 the wattless component of the voltage across the terminals of the 

 fan motor in problem 25. Ans. (a) Power component 0.533 

 amperes, wattless component 0.893 amperes ; (&) power com- 

 ponent 32.8 volts, wattless component 54.95 volts. 



CHAPTER IV. FUNDAMENTAL PROBLEMS. 



31. A harmonic alternating current, maximum value 100 

 amperes, frequency 60 cycles per second, flows through a circuit 

 consisting of a non-inductive resistance of 2 ohms, a resistance- 

 less inductance of 0.003 henry, and a condenser of which the 

 capacity is 0.00006 farad, all connected in series. Draw a clock 

 diagram representing the phases of the electromotive forces across 

 the resistance, across the inductance and across the condenser, 

 respectively, and calculate the effective value of each. Ans. 

 141.4 volts across the resistance, 79.97 volts across the induc- 

 tance, and 3,126 volts across the condenser. 



