Electrical Machines
In dc machines, the field system has to be provided on stator unlike synchronous machines Where in it could be on any member, because

 commutator action is not possible otherwise
 it reduces field structure iron losses
 dc machines are comparatively low rating machines.
 it gives more uniform air-gap flux distribution

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Electrical Machines
For an ideal transformer the winding should have

 minimum resistance on primary side and maximum resistance on secondary side
 maximum resistance on primary side and least resistance on secondary side
 no ohmic resistance on either side
 equal resistance on primary and secondary side

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