Electrical Machines
A 230 V, 50 Hz, 4 pole single phase induction motor is rotating in the clockwise ( forward ) direction at a speed of 1425 rpm. If the rotor resistance at standstill is 7.8 Ω. Then the effective rotor resistance in the backward branch of the equivalent circuit will be

  4 Ω.
 8 Ω.
 10 Ω.
  2 Ω.

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

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