DIRECT-CURRENT DYNAMOS AND MOTORS. 
Lt. 
18. 
19. 
20. 
21. 
22. 
23. 
24. 
Give the average electrical efficiency of a 3 H. P. motor. 
What is the average commercial efficiency of a 35 H. P 
motor? 
State the four principal forms of armatures. 
Which of the four types of armatures referred to in the ‘pre- 
ceding question are most used? Give also the scope of 
the other types. 
Name the chief advantage of the ring type of armature. 
State the advantage of formed armature coils. 
What is the principal advantage of the drum type of arma- 
ture? 
What is the latest practice in the selection of the type for 
an armature? 
What is the object of laminating the armature core? 
In which direction should the armature core be laminated 
relative to the direction of the magnetic flux and to the 
direction of rotation? 
State the disadvantages of armature cores built of iron wire. 
How are the core discs arranged in armatures of small and 
of large sizes? 
What is the usual thickness of the sheet iron employed for 
core discs? 
How are the core lamingw insulated from each other? 
How does the lamination of the armature core affect its 
magnetic carrying capacity? 
