18 
DIRECT-CURRENT DYNAMOS AND~MOTORS..: .:: 
185. 
186. 
18%. 
188. 
189. 
190. 
191. 
(192. 
193. 
194. 
195. 
196. 
19%. 
What is the eddy current factor, and upon what does its 
magnitude depend? 
Give the eddy current factor for sheet iron, 20 mils thick, 
at a flux density of 94,000 lines per square inch. 
What is the eddy current factor for .012-inch sheet iron 
at 85,000 lines per square inch? 
Compute the eddy current factor at 88,000 lines for a 
thickness of lamination of =; inch. 
How is the specific power loss in the armature obtained? 
Tabulate the average temperature increase of drum and 
ring armatures corresponding to various values of the 
specific cooling surface. 
What is the probable average temperature rise of a ring 
armature, for which the value of the specific cooling 
surface has been found to be .85? 
What is meant by the circumferential current density of 
an armature? 
Give the formula for the circumferential current density 
of any armature. 
Compile the average values of the temperature rise cor- 
responding to various values of the circumferential 
current density. 
If the circumferential current density of a high-speed 
armature has been found to be ¢ = 335, what will be 
the probable average temperature rise ? 
Find the probable temperature increase of a bipolar drum 
armature of which the following data are known : 
Output (constant potential), 250 volts, 100 amperes; 
speed, 1,300 revs. per min.; diameter, 3 inches; length, 
163 inches; inside diameter of disc, 34 inches; thickness 
of sheet iron, .020 inch; winding, 66 coils of 2 turns of 
No. 6 B. & 8. wire; resistance, at 20° C., .06 ohm. 
Predetermine the approximate average temperature rise 
