DC Motor or Direct Current Motor Multiple Choice Questions and Answers

11. The commentators segments of d.c. machine are made up of .......

   A.Stainless steel

   B.Hard drawn copper

   C.Brass

   D.Bronze

12. In a d.c. machine, Interpoles are used to .......

   A.Neutralise the effect of armature reaction in the Interpol region

   B.Generate more induced EMF in the armature

   C.Avoid interference of the armature flux with the main field flux

   D.Reduce the demagnetising effect of armature reaction

13. Aluminium is not used as winding wire for the armature of DC machine because .........

   A.Aluminium has low resistivity

   B.A large winding space is taken by aluminium conductors and creates jointing problems

   C.The thermal conductivity of aluminium is low

   C.Aluminium has low conductivity as compared to copper

14. The counter EMF of a DC motor ......

   A.Often exceeds the supply voltage

   B.Aids the applied voltage

   C.Helps in energy conversion

   D.Regulates its armature voltage

15. The mechanical power developed by the armature of a d.c. motor is equal to .......

   A.Armature current multiplied by back emf

   B.Power input minus losses

   C.Power output multiplied by efficiency

   D.Power output plus iron losses

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