DC Motors
The running speed of a dc series motor is basically determined by

None of the listed here
Load
Field excitation
Armature reaction

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DC Motors
If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens

This will make armature to take heavy current, possibly burning it
This will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
Motor will run at very slow speed
Nothing will happen to the motor

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