DC Motors MCQs

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The speed of a dc motor is

  • A. directly proportional to back emf and inversely proportional to flux
  • B. inversely proportional to back emf and directly proportional to flux
  • C. directly proportional to emf as well as flux
  • D. inversely proportional to emf as well as flux
  • Correct Answer: Option A

Condition for maximum power output for a dc motor is

  • A. Eb = V
  • B. Eb = V/2
  • C. Eb = IaRa
  • D. Eb = 1/2 IaRa
  • Correct Answer: Option B

Terminal voltage equation for dc motor

  • A. V = Eb IaRa
  • B. V = Eb - IaRa
  • C. Eb = V IaRa
  • D. Eb = V - IaRa
  • Correct Answer: Option A

Carbon brushes are used in electric motors to

  • A. brush off carbon deposits on the commutator
  • B. provide a path for flow of current
  • C. prevent overheating of armature windings
  • D. prevent sparking during commutation
  • Correct Answer: Option B

The function of the commutator in a dc machine is

  • A. to change alternating current to direct current
  • B. to improve commutation
  • C. for easy speed control
  • D. to change alternating voltage to direct voltage
  • Correct Answer: Option D

The rotating part of a dc motor is known as

  • A. pole
  • B. stator
  • C. armature
  • D. carbon brush
  • Correct Answer: Option C

What is the effect produced by the electric motor?

  • A. magnetic effect only
  • B. magnetic as well as heating effect
  • C. heating effect only
  • D. heating as well as chemical effect
  • Correct Answer: Option B