DC Motors
A dc motor is still used in industrial applications because it

Is cheap
Is simple in construction
Provides fine speed control
None of the listed here

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

Motor will run at very slow speed
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
Nothing will happen to the motor

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