DIRECT CURRENT. DYNAMOS AND MOTORS. | 17 
170. A 6 pole ring armature having an external diameter of 42 
inches, an internal diameter of 34 inches, and a length 
of 11 inches. is wound spirally with 600 turns of 2 No. 
6 B. & S. wires, in two layers. Find its resistance at 
60° C. | 
171. What would be the resistance of the armature in the pre- 
ceding example, if it were wound with 1,200 turns of 
1 No. 6 B. & S. wire so as to give double its previous 
voltage in a 4-pule field? 
172. How can the armature design be checked with reference 
to the heating limit? 
173. If the temperature increase of the armature is found 
excessive, how must the armature be re-designed ? 
174. Give formula for computing the power loss in the arma- 
| ture winding. 
175. How can the exact amount of the shunt current in a 
completed machine be computed? 
176. Tabulate the average factors by which the external cur- 
rent of shunt and compound wound generators and 
motors of various capacities must be multiplied, in — 
order to obtain the current flowing in the armature. | 
177%. What is the formula for the power loss by hysteresis? 
178. What does the hysteresis factor express? 
179. How can the hysteresis factor for any given flux density 
be calculated? 
180.. What is the value of the hysteresis factor for a flux den- 
sity of 77,500 lines per square inch? 
181. Find the hysteresis factor for a density of 142,000 lines 
per square inch. 
182. How is the frequency of a dynamo obtained? 
183. Give formula for the mass of the armature core. 
184. By what formula is the power loss by eddy currents 
calculated ? 
