Electrical Machines
If the back emf in DC motor vanishes suddenly the motor will

 run at very low speed.
 start haunting.
 run at very high speed.
 burn.

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Electrical Machines
In a DC machine

 current and emf in armature are alternating.
 current and emf at the terminals are alternating.
 current and emf in armature are unidirectional
 emf in armature conductors and at the terminals is alternating.

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Electrical Machines
In case of 3 - Φ IM, plugging means

  starting the motor on load which is more than the rated load.
  locking of rotor due to harmonics.
  interchanging two supply phases for quick stopping.
  pulling the motor directly on line without a rotor.

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