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The induced EMF in an inductor

  1. Feb 26, 2017 #1
    1. The problem statement, all variables and given/known data
    A generator consists of 500 turns each of surface area 7/11 m² . It rotates at rate of 50 revolutions per second (f =50 Hz), in a field of magnetic flux density of 5*10^-4 T, its terminals were connected in series with a capcitor (Xc=110Ω), an inductor (Xl=80Ω) and a resistor (R=40Ω).

    Ignoring the internal resistance of the generator, the maximum induced emf in the inductor is:
    a) 30V. b) 40V. c)50V. d) 60V

    2. Relevant equations
    emf= NBAω
    emf(eff)= 1/√2 emf(max)
    Z= √R²+(Xl-Xc)²

    3. The attempt at a solution
    Here is it, and the final solution I got is not any of the choices, so please correct me, and tell me where I am wrong.
    iGRhD.jpg
     
  2. jcsd
  3. Feb 26, 2017 #2
    This thread has been marked solved, although the answer I got of my work is not any of the choices, and it is MCQ. So, is there any explanation here?
     
  4. Feb 26, 2017 #3

    cnh1995

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    Homework Helper

    Your method looks correct but you have calculated the rms value of induced emf in the inductor.
    But the peak value is also not in the options.
     
  5. Feb 26, 2017 #4

    gneill

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    Staff: Mentor

    I wonder if the question was first formulated to ask for the maximum voltage across the resistor and was subsequently changed to be the inductor in order to make a "new" question, but whoever did it forgot to change the answer choices accordingly?
     
  6. Feb 26, 2017 #5

    gneill

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    Staff: Mentor

    No, the thread has not been marked solved. Perhaps you saw the icon at the top right of the thread:

    upload_2017-2-26_10-57-37.png
    and concluded that it had been marked solved? That icon is actually a button for you to click on once you've decided that the problem has been solved to your satisfaction.

    If the thread was actually marked solved then that button would read "MARK UNSOLVED", and you could retract the solved status by clicking on it. Hope that helps :smile:
     
  7. Feb 26, 2017 #6
    Do you mean that I shouldn't calculate the rms of the induced emf of the generator? And hence I would get the correct value of the induced emf in the inductor?! Which would be 80V?
    Gneill, actually that is how the question is found in my textbook.
    Oops, how silly I am, I didn't even notice that it was a button, thank you gneill!
     
  8. Feb 26, 2017 #7

    cnh1995

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    Yes, because you need the peak voltage.
    Yes, I think so.
    Might be a typo.
     
  9. Feb 26, 2017 #8
    Perhaps.
    OK, I will take your advice.
     
  10. Feb 26, 2017 #9

    rude man

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    Gold Member

    I'd go with 80 also.
     
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