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Homework Help: Can someone check my Physics working?

  1. Apr 26, 2004 #1
    Hi all,
    can somebody pls check whether or not I'm in the right direction with my workings and answers. If not, can you pls advise why I've gone wrong?

    thanks

    question 1:
    1. An inductor has a 54 ohm reactance at 60 Hz. What is the maximum current if this inductor is connected to a 50 Hz source that produces a 100 Vrms voltage?

    answer:
    L=?
    XL = (2 pie f)(L)
    54 = (2 pie 60) L
    L = 54 / (2 pie 60) = 0.14H

    Imax = ?
    f = 50 Hz
    Vrms = 100V
    V max = 100 * sq root of 2

    XL = wL
    = (2 pie 50) (0.14)
    = 43.98 = 44 ohm

    therefore
    Imax = Vmax / XL
    = (100 * sq root 2) / 44 = 3.2A

    question 2:

    What maximum current is delivered by a 2.2 microF capacitor when connected to a North American outlet where Vrms = 110 V and f = 60 Hz

    answer
    Imax = ?
    Xc = 1 / (wC) = 1 / [(2 pie 60) * (2.2E-6)]
    = 1206 ohm
    Imax = Vmax / Xc
    = (110 * sq root of 2) / 1206
    = 0.13A

    thanks again
    cseet
     
  2. jcsd
  3. Apr 28, 2004 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Looks good to me.

    The only thing I could suggest is that when you wish to give your answer to 2 significant figures (which is great!) to be sure to carry all intermediate calculations to at least 3 figures to minimize any round off error. For example, in problem #1 you round off the inductance to 0.14 when a more accurate answer is 0.143. Wait until the last step to round off your answer to a sensible number of figures.
     
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