CHAPTER XV 

 MOTORS 



1. A wire 40 cm. long and carrying 100 amperes lies in a field 

 of 5000 gausses. Required the force acting on the wire in dynes. 

 (1 min.) 



2. A 2-pole motor has an armature diameter of 8 inches and 

 an armature length of 10 inches; the polar angle is 120 degrees 

 and the width of the pole is equal to the armature length; th'-n- 

 are 220 conductors and the density in the gap is 4500. Required 

 the horse-power converted by the motor at 1200 r.p.m., and when 

 taking 40 amperes in the armature. (Neglect the fringing.) 

 (5 min.) 



3. The following data refer to a 4-pole, 4-path, 220-volt motor 

 taking 140 amperes in its armature and running at 750 r.p.m.: 



Armature diameter 15 inches 



Armature length 11 niches 



Armature conductors 300 



Polar angle 72 degrees 



Gap density 7500 



Required the horse-power converted and also the horse-power 

 output, if the iron losses constitute 3% and the friction loss 2% 

 of the output. (7 min.) 



4. What horse-power is being converted by a motor having 

 124 conductors on a 6" X 6" armature, the poles covering 120 

 degrees each, and the total flux being 1.94 X 10 6 when the arma- 

 ture current is 22 amperes, and the speed is 1500 r.p.m. (S min.) 



6. A shunt motor has 220 volts applied and takes 52.2 amperes. 

 The field resistance is 110 ohms and the armature resistance is 

 0.2 ohm. Required the counter e.m.f. Also if the total flux is 

 2.72 X 10 6 , and the number of conductors 300, required the number 

 of revolutions per minute. (3 min.) 



6. A shunt motor on a 110-volt circuit, having an armature 

 resistance of 0.25 ohm, runs on no load at 1150 r.p.m., and at a 

 full load of 30 amperes at 1120. With 30 amperes how much 



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