28 
DIRECT-CURRENT DYNAMOS AND MOTORS. 
27%. 
238. 
279. 
280. 
281. 
282. 
283. 
284. 
285. 
286. 
28%. 
288. 
289. 
What is the formula for the ampere-turns of‘an iron } at h, 
in English units? 
State the formula for the ampere-turns of an air path, if 
its length and density are given in metric units. 
Give the expression for the ampere-turns of an air path iti 
English units. 
‘Define specific magnetizing force, 
Give formula for the ampere-turns required for any por- 
tion of a magnetic circuit, if its length and specific 
magnetizing force are given. 
State an approximate rule, used in preliminary calcula- 
tions, for finding the ampere-turns required foe com. 
pensating armature reaction. 
Inspect closely the magnetizing curves of annealed 
wrought iron and ordinary cast iron (Fig. 27, Instruc- 
tion Book), noting three or four characteristic points 
on each curve, and then plot these curves by locating 
the points so noted in a roughly drawn co-ordinate sys- 
tem and connecting the same by free hand. 
What is the specific magnetizing force for soft cast steei 
at a density of 55,000 lines per square inch? 
Give the specific magnetizing force of annealed wrought 
iron, if its density is 106,000 lines per square inch. 
From Table 26, Instruction Book, determine the ampere- 
turns required for 25 inches of soft cast steel, if the 
density is 92,500 lines per square inch. 
State the influence of the armature current upon the mag- 
netic field. 
Give formula for the demagnetizing number of ampere- 
turns of a smooth armature. 
How can the angle of field distortion be approximately 
determined in case of a smooth armature? 
