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Question 20248
JEE Physics · Medium

Electromagnetic Induction and Alternating Current: Back EMF — Starting Current MCQ

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Back EMF — Starting CurrentMediumQuestion 20248

Question

DC motors draw very high current at startup because:
  1. A
    Back EMF is maximum at startup
  2. B
    Back EMF is zero at startup (zero speed) so only resistance limits current
    Correct
  3. C
    Inductance is very high at startup
  4. D
    Supply voltage is highest at startup

Correct answer

Back EMF is zero at startup (zero speed) so only resistance limits current

Explanation

At rest, ω = 0 → back EMF = 0. Supply current = V/R_armature. Since R_armature is small, startup current = V/R is very large. Starter resistors are used in series to limit this initial current.

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