Electrical Machines
Autotransformer makes effective saving on copper and copper losses, when its transformation ratio is equal to

  greater than one.
  very low
  approx to one.
  less than one.

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Electrical Machines
In speed control of DC Series motor, speed lower than the rated speed can be obtained by

 Connecting an additional resistance in the field circuit.
 Any of the above.
 Connecting an additional resistance in stator circuit.
 Connecting an additional resistance in the armature circuit.

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Electrical Machines
In a DC machine the armature mmf is

 rotating with respect to field poles.
  rotating with respect to field poles as well as armature.
  stationary with respect to field poles.
  stationary with respect to armature.

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