DC Motors
In case the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be

1
Around 90%
Anywhere between 75% and 90%
Less than 50%

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DC Motors
As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit

A resistance is connected in series with armature
A high value resistor is connected across the field winding
A resistance is connected parallel to the armature
Armature is temporarily open circuited

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