56 ELECTRICAL ENGINEERING PROBLEMS 



10. If a milliammeter with inductance in series be used as a 

 frequency meter, upon a circuit of constant e.m.f . of 120 volts, and 

 if the resistance is negligible and the inductance is 10, what current 

 will indicate a frequency of 60 periods? (2 ram.) 



11. Given E, 127; r, 40; I, 1.54; and the frequency, 115; 

 required the reactance, inductance and angle of lag. (6 ram.) 



12. Given E, 1100; -I, 6.54; r, 86; and the frequency, 115; 

 required the reactance and inductance. (6 ram.) 



13. Given an impressed e.m.f. of 100; r, 5; and 1, 12; determine 

 the value of L and the induced e.m.f. if the frequency is 63. 

 (3 mm.) 



14. Required the e.m.f. to send 10 amperes through a circuit 

 with 3 ohms if the e.m.f. of inductance is 20. (1 ram.) 



15. Given for a coil of wire r, 40 and L, 0.05; if the frequency 

 is 95.5, required the angle of lag as defined by the tangent and 

 the e.m.f. necessary to send 10 amperes through. Construct the 

 angle of lag. (6 ram.) 



16. An inductive circuit having a resistance of 2 ohms carries 

 10 amperes, maximum, and an inductive e.m.f. of 10 volts maxi- 

 mum is set up in the circuit. Construct the sine curves for active 

 e.m.f. and induced e.m.f. and from these derive and construct the 

 curve of impressed e.m.f. (10 mm.) 



17. A circuit of 5 ohms resistance carries 20 amperes maximum; 

 an inductive e.m.f. of 30 volts is set up in the circuit. Construct 

 the e.m.f. parallelogram for this case, and by revolution of this 

 construct the sine curves for the active, induced and impressed 

 e.m.f. 's. (10 ram.) 



18. Given for a circuit resistance 4 ohms, maximum current 

 20 amperes, maximum inductive e.m.f. 20 volts; construct e.m.f. 

 curves, including the impressed e.m.f., and from these the parallelo- 

 gram of e.m.f.'s. (10 mm.) 



19. Given an effective current of 20 amperes in a circuit whose 

 resistance is 4 and reactance 2 ohms; plot the curves of active and 

 induced e.m.f. and from them the curve of impressed e.m.f. Also 

 construct the e.m.f. parallelogram which would generate these 

 curves. (10 mm.) 



20. In a circuit of 10 ohms and 0.005 henry, what is the largest 

 value that the frequency can have, without producing a decrease 

 of more than 1% in the current which flows when the frequency 

 is zero? (5 mm.) 



