DIRECT-CURRENT DYNAMOS AND MOTORS. 23 
223. Give formula for the cross-section of the field frame, and 
state the meaning of the symbols used. 
224. What are the usual limits of the leakage factor for bipolar 
; toothed-armature machines? 
225. Between what limits does the leakage factor ordinarily 
range in bipolar smooth armature machines? 
226. Give the usual range of the leakage factor for multipolar 
ring-type machines having a toothed armature. 
22%. Between what values does the leakage factor of multi- 
polar smooth-armature dynamos usually vary? 
228. State the limits between which the flux density for 
wrought iron and cast steel should be chosen. 
229. What are the best values of the flux density in cast iron? 
230. How is the core area of a multipolar machine obtained 
from the formula referred to in Question 223? 
231. By what number must the total frame area of a multi- 
polar ring-type dynamo be divided to give the cross- 
section of the yoke? 
232. What relation does the yoke-section usually bear to the 
core-section in multipolar types, if the same material is 
used for both? 
233. Show a multipolar type in which the yoke-section is equal 
to the core-section. 
234. What is the usual relation between core-area and yoke- 
area in the bipolar types, provided that cores and yoke 
are of the same material? 
235. Sketch a bipolar type in which the yoke-section is only 
one half the core-section. 
236. Tabulate the average values of the leakage factor for the 
various sizes of the most common types of dynamos, 
according to Tahle 24, Instruction Book. 
