50 ELECTRICAL ENGINEERING PROBLEMS 



26. The shunt field of a 110-volt dynamo has a resistance of 

 42 ohms and an inductance of 12 henries. If 100 volts be applied 

 to the terminals, how long will it take the current to reach 0.95 

 of its maximum value? How long to reach 0.99? (4 ram.) 



27. A circuit has an inductance of 100 henries. Plot curves of 

 current rise with an applied constant e.m.f. of 100 volts for the 

 following resistances, 1, 10, 100 and 1000 ohms. Use different 

 scales so as to bring the final current value the same in each case. 

 (30 min.) 



28. If the exciting current at 110 volts in problem 26 be broken 

 in 3& of a second and the current thereby reduced to zero, what 

 e.m.f. will exist between the terminals? (1 ram.) 



29. Two coils, A and B, lie in parallel planes; 60%- of the lines 

 produced by one coil thread through the other. Five amperes 

 through the coil A produces a flux of 5000 in A. If the current 

 in A change from +6 to 6 amperes in 0.01 second, what will be 

 the e.m.f. produced in coil B, if B have 1000 turns? What is the 

 mutual inductance? (3 ram.) 



