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A.C problems[please help]

  1. Jan 21, 2007 #1



    Our teacher give us a EX. but I don't how to do .
    The teacher ONLY give us a week time to finish it .
    I realy hope that some one can help me !

    (I ONLY KNOW Q1c & Q2a)
  2. jcsd
  3. Jan 21, 2007 #2


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    Homework Helper

    there is quite a lot there... If you don't even know how to do Q1a, then you really need to first learn about phasors, how to convert capacitance/inductance into reactance etc, .... by the sound of it I think you are lacking a lot of the basics, so much that I do not actually recommend tackling these problems for there are quite a lot concepts involved... should first learn the basics... either read your lecture notes...if they happens to be crap :smile: ...then may be try

    Hambley, Electrical Engineering (principles and applications)
    Cheng, Field and waves electromagnetics
    Nilssonn & Riedel, Electrical Circuits
    (see topics related to Steady-state sinusoidal analysis)
  4. Jan 21, 2007 #3
    You should get your concepts cleared first, but here are the answers to the first question:

    a. v=200sin(200pi t), This is of the form v=asin(wt) where w=200pi.
    Capacitive reactance Xc=1/wcand[tex]Impedence=\sqrt(Xc^2+R^2)[/tex]
    b. Vmax=200
    d. Use ohm's law.
    e. You have the equation of current varying with time and you know that current and voltage are 90 out of phase...
  5. Jan 21, 2007 #4
    you need to show your efforts on the problems before we can help you.
  6. Jan 21, 2007 #5
  7. Jan 22, 2007 #6

    a) I find that in book is
    Z^2 = R^2 + 1/(w^2 c^2)
    w=200pi ???

    b)Vmax=200 AS V=Vo sin(200pi t) ,where Vo=200 , right ???

    c)PHASE DIFF. is 90"

    V = I R
    Vosin(wt)= I R
    I = ( Vo/R ) sin wt
    I = Io sin wt

    right ?

    applied voltage = 200V
    voltage across the capacitor at that instant = 0 V
    Last edited: Jan 22, 2007
  8. Jan 22, 2007 #7
    I have just go to this WEB.
    It seem useful !

    100c & 240VR
    Vz^2 = 160^2 + 100^2
    Vz =260 ?

    b) I don't know
    Can you give me some tips ?
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