Electrical Machines
Copper brushes in DC machine are used

 where high voltage and low current.
None of these
 where low voltage and high currents are involved.
 in both of above cases.

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Electrical Machines
No load primary current in a transformer

 leads the applied voltage somewhat less than 90Ã&
 lags behind applied voltage somewhat less than 90Ã
 leads the applied voltage by exactly 90Â&
 lags behind applied voltage by exactly 90Â&am

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Electrical Machines
If the frequency of input voltage of a transformer is increased keeping the magnitude of voltage unchanged, then

 Ph will increase but Pe will decrease
 both hysteresis loss(Ph) and eddy current loss(Pe) will increase
 Pe will increase but Ph will decrease
 Ph will decrease but Pe will remain same

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Electrical Machines
For a single phase capacitor start induction motor which of the following is valid?

 Direction of rotation cannot be changed.
 None of these.
 Rotation can be changed by interchanging supply terminals.
  Rotation can be changed by reversing main winding terminals.

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