DC Motors
The dirction of rotation of a dc series motor can be changed by

None of the listed here
Interchanging field terminals
Either of Interchanging field or Interchanging supply
Interchanging supply terminals

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

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