16 
DIRECT-CURRENT DYNAMOS AND MOTORS. 
158. 
167... 
168. 
169. 
192 slots, 6 conductors per slot. Compute the approxi- 
mate total length of wire. 
If a wire having a resistance of 16 ohms is divided into 8 
equal par.s, what is the joint resistance of the 8 pieces. 
of wire when connected in parallel? 
Express the armature resistance in terms of the total 
resistance of the armature wire and of the number of 
bifurcations. 
Give the formula for computing the armature resistance 
from the total length of wire on the armature. 
What is meant by the resistivity of a wire? 
How is the resistivity at a temperature higher than 20° C. 
found? ; 
What is the rule for computing the resistivity of a warm 
wire, when the temperature is given in Fahrenheit. . 
degrees ? 
By what factor must the resistivity at 68° F. be multiplied 
to obtain the resistivity at 140° F.? 
What is the resistivity of No. 9 B. & S. wire at 50° C.? 
Find the resistance at 80° C. of the armature given in 
Example 151, if each conductor consists of 4 No. 13. 
B. & §. wires. 
What will be the resistance in the previous case, if the 
armature, in order to produce double the voltage and 
one-half the current output, is connected upso tht each 
conductor consists of only 2 No. 13 wires? 
Give the resistance of the armature referred to in Ques- 
tion 166 for the case that it is wound in 4 parallel cir- 
cuits suitable for a 4-pole field. 
Compute the resistance at 76° C. of a bipolar drum arma- 
ture 23? inches in diameter, 26$ inches long, and wound. 
with 49 coils, each coil consisting of 1 turn of 20 No. 
7B. & S. wires. 
