DIRECT-CURRENT DYNAMCS AND MOTORS. 
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What peripheral velocity should be chosen for a 400 K.. W. 
low-speed direct-connected machine? 
State the approximate velocity of a 600 K. W. medium-speed 
ring armature. 
Give the approximate peripheral speed of a 25 K. W. drum 
armature. 
Name the kinds and sizes of machines for which 3,000 feet 
per minute is a good value for the peripheral velocity. 
Define the cooling surface of an armature. 
What portion of its surface do we consider the cooling area 
of adrum armature? Why not the entire surface of the 
core? 
Give the formula for the cooling surface of a drum armature 
in terms of its diameter and length. 
Whatis the formula for the cooling surface of a drum arma- 
ture, expressed in terms of its diameter and shape ratio? 
What area is usually considered the cooling surface of a 
ring armature? 
Give the formula for the usual case of the cooling surface 
of a ring armature, if all its dimensions are given. 
What formula is used for the cooling surface of a ring ar- 
mature, if only its diameter is given and its shape ratios 
are assumed? 
How much cooling surface is needed to dissipate the heat 
corresponding to 1 watt of power loss? | 
Give the formula for the cooling surface required for a 
dynamo having a capacity of W wats. 
