CHAPTER VII 



GENERATION OF ELECTROMOTIVE FORCE 

 ARMATURE DROP 



1. Required the e.m.f. in volts of a conductor 18 cm. long, 

 cutting a field of B, 9000, at a velocity of 1200 meters per minute. 

 Q min.) 



2. A conductor on the surface of an armature is 50 cm. long 

 and cuts through the magnetic field of density 9000 under a pole 

 piece; the speed is 27 meters per second. What e.m.f. will be set 

 up in it? (1 min.) 



3. A rectangular coil having 85 turns, 20 X 40 cm., is moved 

 in the direction of its long axis through a magnetic field at the rate 

 of 12 meters per second. One of its short sides is outside of the 

 field. The terminals of the coil are connected to an oscillograph 

 which shows that the e.m.f. set up is 0.012 volts. What is the 

 density of the field? (1 min.} 



4. If the coil of the last problem were moved in a direction 

 making 30 degrees with the axis of a field of density 8000, what 

 would be the e.m.f. set up? (1 min.) 



5. A 1-kw., 2-pole generator has 228 conductors and a speed of 

 2000 r.p.m. The flux is 1.6 X 10 6 maxwells; what is the e.m.f.? 

 (1 min.) 



6. A 2-pole, 8-kw., 125-volt generator has 180 conductors. 

 The flux is 2.5 X 10 6 . At what r.p.m. must the generator be run? 

 (1 min.) 



7. A 1000-kw., 16-pole, 500-volt generator is to run at 90 r.p.m. 

 There are 2304 conductors. What must be the flux per pole, and 

 what the area of the pole pieces with an air-gap density of 8600? 

 (2 min.) 



8. The copper loss in the armature of problem 7 is 24 kw. 

 What increased voltage would the machine generate at full load in 

 order to give 500 volts, at the terminals, and what per cent increase 

 in the flux would be necessary? (1 min.) 



9. There are 100 complete turns on a bipolar armature which 



18 



