The efficiency of a dc series machine cannot be determined by Swinburne's test as
A series motor runs at dangerously high speed on no load
A dc shunt motor is driving a constant torque load with normal excitation. If the filed current is halved then the motor will run at
A dc shunt motor is driving a mechanical load at rated voltage with normal excitation. If the load torque is increased to double of the normal one, the speed of the motor will