DC Motors
The iron loss in dc motor depends on

Both flux and speed
Speed only
None of the listed here
Flux only

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

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

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