Electrical Machines
The brush-axis of a bipolar dc motor is rotated by 90°. The effect of this rotation on the back emf Eband the torque developed Tdwould be such that

 both Eb and Td are unchanged
 both Eb and Td are zero
 Eb is zero, but Td is unchanged
 Eb is unchanged, but Td is zero

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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)

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

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Electrical Machines
Two dc machines A and B, using the same conductor material, have armature circuit resistances of 0.4 Ω and 1.2 Ω respectively. Of the two machines,

 B is bigger than A for the same current rating
 A is bigger than B for the same voltage rating
 both are of the same size for the same current rating
 A is bigger than B for the same current rating

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