DC Motors
By putting controller resistance in series with the armature of a dc motor, we can obtain speeds

None of the listed here
Above as well as below the normal speed
Below the normal speed only
Above the normal speed only

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DC Motors
In variable speed motor

A weaker commutating field is needed at low speed than at high speed
Same commutating field is needed at low speed than at high speed
None of these
A stronger commutating field is needed at low speed than at high speed

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

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