380 ELEMENTS OF ELECTRICAL ENGINEERING. 



5. The above repeatedly reversed electromotive force acts on 

 a circuit containing inductance only. The inductance of the cir- 

 cuit is o. I henry. Plot the electromotive force curve and the 

 current curve, and find (a) the average current during half a 

 cycle and (b) the effective current. Ans. (a) 2.5 amperes, (b) 

 2.89 amperes. 



N t e , The value 2.89 is found by dividing the half-cycle into 10 equal parts and 

 measuring the middle ordinate of each part. 



The current curve which is required in this problem is strictly indeterminate. Alj 

 that is known from the given data is that the current increases (or decreases) by the 

 amount of IO amperes during the time that the electromotive force acts in a given 

 direction. Plot the current curve on the assumption that the maximum positive and 

 negative values of the current are equal to each other. 



6. An electromotive force which is represented by the curve 

 in Fig. 6p, acts on a circuit which contains a condenser only. 



i/ioo second ' 



Fig. 6A 



The capacity of the condenser is 10 microfarads. Plot the cur- 

 rent curve and find (a) the average current during half a cycle and 

 (b) the effective current. Ans. (a) 0.2 amperes, (b) 0.2 amperes. 



Note. The current is in this case at each instant equal to the product of the 

 capacity in farads times the rate of change of the electromotive force. 



7. If the frequency of the electromotive force were doubled in 

 problems 5 and 6, how would the effective current be changed in 

 each case ? Ans. In problem 5 the effective current would be 

 reduced to one half, and in problem 6 the effective current would 

 be doubled. 



Note. It is important that the physical argument of this problem be given by 

 the student. 



8. A two-pole alternator, having one conductor on its armature, 

 has pole pieces shaped as shown in Fig. 8/. The total flux 

 emanating from the TV pole is 1,000,000 lines, and the armature 



