ALTERNATING CURRENT IN INDUCTIVE CIRCUITS 57 



21. An instrument for use on a circuit with , 400 (frequency, 

 63.7) has r, 1000, and L, 1. What per cent increase of frequency 

 would cause an error of 1%? (7 win.) 



* 22. Given a laminated ring 30 cm. in circumference, 3 cm. in 

 diameter of cross-section and having /z = 2000, at a density of 

 B = 6000; required the number of turns to give L = 0.1. (4min.) 



23. Given for an inductive circuit r, 5; L, 0.01; E, 75; and I. 

 11.8; required the frequency. (4 win.) 



* 24. A solenoid of 800 turns, 1 meter long and 5 cm. in diani' 

 has r, 0.15 ohm; required the inductance and the current when a 

 10-volt, 75-period current is applied, and also the angle of lag. 

 What would the current be if the same wire were wound imn- 

 inductively? If the frequency be doubled, what will be the cur- 

 rent and the angle of lag? (15 win.) 



25. Given for an inductive circuit r, 40.4; L, 0.101; frequ* 

 100; and I, 1.34; required the impedance, the e.m.f. and the angle 

 of lag. (7 win.) 



< 26. A circuit has 0.025 henry and a variable resistance. 11.") 

 volts having a periodicity of 58 is applied; construct the locus of 

 the current vector, and show graphically that it is correct for two 

 cases. (5 win.) 



* 27. A circuit on a 100-volt system has a resistance of 5 ohms. 

 Plot the locus of current with varying reactance. Note that the 

 change in reactance may be due either to change in inductance or 

 frequency, so that the same curve could be used for either. (5 

 win.) 



' 28. A condenser of 50 microfarads capacity is connected to 

 a 60-period, 110- volt circuit. What charging current will flow? 

 What will it become on 1100 volts. What will be the ratio of 

 volt-amperes in the two cases? (4 win.) 



29. If the condenser of problem 28 is used on a 1200-period, 

 1100- volt circuit, what will the charging current be? What will 

 be the capacity reactance? (3 win.) 



* 30. A 25-period, 100,000-volt, 110-milo transmission line has 

 an equivalent capacity of 0.01 microfarad per mile. What will 

 be the charging current and the charging kilovolt-amperes? What 

 is the capacity reactance? (3 win.) 



31. A 100-microfarad condenser is connected to an alternating- 

 current generator having co, 400, through a line of negligible 

 resistance; the maximum current is 8. Plot sine curves of current 



