DC Motors
In dc machines fractional pitch winding is used

To reduce the sparking
To reduce the generated emf
To improve cooling
To increase the generated emf

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DC Motors
If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens

This will make armature to take heavy current, possibly burning it
Motor will come to stop
This will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
Nothing will happen to motor

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