DESIGN OF DIRECT-CURRENT 
DYNAMOS AND MOTORS. 
201. What is the almost universal modern practice in regard to 
the adoption of the bipolar and multipolar forms for 
dynamos of various outputs? 
202. Name the advantages of the multipolar form over the 
bipolar. 
203. What are the disadvantages of multipolar machines? 
204. Show the saving of material effected in the multipolar 
construction by comparing a 4-pole frame with a bipo-. 
lar frame for the same armature. 
205. Compare in the same manner as in the preceding question 
an 8 pole machine with an equivalent oneof the bipolar 
type. 
206. If a total flux of 2,400,000 lines is required for an arma- 
ture of given diameter, what must be the carrying 
capacity of the armature cross-section for a bipolar, 
4-pole, and 8-pole machine, respectively ? 
20%. Neglecting magnetic leakage, how many lines are carried 
by eich magnet core and by the yoke section of the 
bipolar, 4 pole, and 8-pole construction in the case con- 
sidered in the preceding question? 
208. Give the formula for the frequency of magnetic reversal 
in a dynamo-electric machine. 
209. What. is the frequency of.an 8-pole machine when running’: 
at 500 revolutions per minute? 
