DIRECT-CURRENT DYNAMOS AND MOTORS. ‘13 
124. Give the formula for the total E. M. F. generated in an 
armature. 
125. By transformation of the EK. M. F. formula referred to in 
the preceding question, give the expression for the 
length of armature inductor required to produce a cer- 
tain voltage. 
126. Upon what does the gap induction iu a dynamo depend? 
12%. How can Table 16 be used for machines in which a strong 
field is desired ? 
128. How is Table 16 used in case of electroplating ma- 
chines, battery motors, and incandescent generators? 
129. From Table 16 find the approximate gap density for a 25 
K. W. smooth armature bipolar dynamo having cast 
iron polepieces. 
130. What field density should be hone for the machine re- 
ferred to in the preceding question, if it had a toothed 
armature and cast steel pole shoes? 
131. Give the average field induction which should be taken 
| for a 50 K. W. multipolar dynamo with smooth arma- 
ture and wrought iron polepieces, if a strong magnetic 
field is required. 
132. What gap density is to be used for a 10,000-light multipo- 
lar incandescent generator having a toothed armature 
and steel polepieces? 
133. Give the average field density employed for the machine 
‘ referred to in the preceding question, in case of a 
smooth-core armature and strong field. 
134. Express the length of the armature core in terms of the 
| number of inductors and of their active length. 
135. If anarmature has N inductors and n, bifurcations, what 
is the number of inductors effective in generating, the 
total voltage? 
136. Give the formula for the armature flux in terms of the 
electrical data of the machine. a al 
