Electrical Machines
A DC shunt machine generates 250 V on open circuit at 1000 RPM. Armature resistance is 0.5 Ω, field resistance 250 Ω. When running as a motor takes 4 A at 250 V. Calculate the efficiency when running as a motor taking 40 A at 250 V. Armature reaction weakens the field by 4%.

 67.5%
 82.5%
 72.5%
 78.5%

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Electrical Machines
What will happen if the the supply terminals are reversed in case of a DC shunt motor?

 The motor will stop.
 The motor will run much faster in the same direction.
 The motor will run at its normal speed in the same direction as before.
 The motor will run in reverse direction.

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