CHAPTER IV 



ALTERNATING CURRENT IN INDUCTIVE CIRCUITS 



1. In a given circuit the resistance is 10, the inductance 0.01 

 and the frequency 60. Required the e.m.f. necessary to cause 2 

 amperes to flow. What current would flow if a cUrect-curn-nt 

 e.m.f. of the same value were applied to the circuit? (3 min.) 



2. In a certain circuit, r = 1, L = 0.01 and w = 400 (frequency 

 = 63.7); required the current and angle of lag if 50 volts are 

 applied. What would be the current if this e.m.f. were direct 

 current? Give the equation for the instantaneous value of the 

 current. (4 min.) 



3. In a certain circuit r is 2 and L is 0.02 and a 100-volt alter- 

 nating e.m.f. gives 10 amperes; required the frequency of this 

 current; also the reactance and impedance of the circuit. (8 min.) 



4. In a certain circuit r is 2 ohms, and with a 200-volt 50-period 

 circuit 50 amperes flow; required the values of the inductance, 

 reactance and impedance. (3 min.) 



6. The exciting current of a 100-volt, 3J-kw. shunt generator 

 field is 2 amperes, and its inductance is 10 henries; required what 

 this current would be if an equal 60-period e.m.f. were applied to 

 it. Also if the alternating current were of 120 periods. (7 min.) 



6. The primary circuit of a 2000-volt, 2-kw. transformer has 

 a resistance of 20 ohms, and an inductance of 40 henries. What 

 current will flow through this coil on a 60-period, 2000-volt circuit, 

 the secondary circuit being open, and what will be the angle of lag. 

 What current would flow with a direct current of equal e.m.f.? 

 Give the equation for instantaneous current values. (6 min.) 



7. A 10-ohm coil is placed upon a 100-volt circuit in which w is 

 400; it is found that the current lags 30 degrees; required the 

 current, the inductance and the reactance of the circuit. (4 min.) 



8. In the circuit of problem 10 the e.m.f. is raised until 200 

 amperes flow, what will it become? (2 min.) 



9. A current of 3000 amperes delivered by a 100-volt trans- 

 former with co = 400, has a power factor of 80%; required the 

 resistance and reactance of the circuit. (3 min.) 



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