DIRECT-CURRENT DYNAMOS AND MOTORS. 29 
290. 
291. 
295. 
296. 
29%. 
How must the formula referred to in Question 2838 ke 
modified in case of a toothed armature? 
What correction is necessary to apply the formula of 
Question 288 to a perforated armature? 
State the average formula for the total number of compen- 
sating ampere-turns in case of wrought iron or cast 
stezl polepieces. 
Give the average formula for the total number of com- 
pensating ampere-turns in case of cast iron polepieces. 
Determine the magnetizing force required for the bipolar 
smooth armature machine shown in answer to Question 
259, provided that the internal diameter of the arma- 
ture discs is 3 inches. 
The magnet frame of a bipolar dynamo is composed of 
wrought iron cores and yoke, and cast iron polepieces; 
the diameter of the cores is 142 inches; the cross-section 
of the yoke is equal to that of the cores; the section of 
the polepieces is 408 square inches, that of the armature 
core is !70 square inches, and the gap area is 440 square 
inches; the length of the magnetic circuit in the cores 
and yoke is 80 inches, in the polepieces 28} inches, in 
the armature 124 inches, and in the air gaps 14 inches; 
the armature flux is 11,000,000 lines; the factor of 
leakage is 1.3; the armature is wound with 50 turns; 
current output, 480 amperes; polar embrace, 75 per 
cent. Compute the exciting power required. 
Find the number of ampere-turns required to excite the 
machine shown in answer to Question 260, assuming 
the density in the tc eth to be 100,000 lines per square 
inch, and the density in the solid portion of the arma- 
ture core, 85,000 lines per square inch. 
Assuming the machine given in Question 266 to be 
wound with 336 armature turns and having a current 
output of 600 amperes, what will be the exciting power 
