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Brushless machines have displaced single-phase induction motors in newer appliances because they

  • A.require no electronic controller of any kind to run
  • B.develop no torque pulsation and need no rotor at all
  • C.can be connected directly to a single-phase supply
  • D.are more efficient and their speed can be varied

Answer: D

A magnet rotor with electronic commutation avoids the backward field, the auxiliary winding and the centrifugal switch, and it can be run at whatever speed the appliance needs. Mass production has made the controller cheap.

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