Electrical Machines
The armature mmf of a DC machine has

  triangular space distribution and is stationary in space.
  trapezoidal space distribution and is stationary in space.
 stepped distribution and rotates at the speed of armature.
  triangular space distribution and rotates at the speed of armature.

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Electrical Machines
If the applied voltage of a certain transformer is increased by 50% and the frequency is reduced by 50%, the maximum flux density will (assuming that the magnetic circuit remains unsaturated)

 changes to 0.5 times the original value
 changes to 1.5 times the original value
 remain the same as the original
 changes to three times the original value

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