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Homework Help: Circuit, capacitance, resonance

  1. Apr 18, 2008 #1
    Hi all;

    So the problem goes as follows:

    [FONT=&quot]For the circuit in the figure, what should be the capacitance C to put the circuit into resonance? What is then the RMS value of the current? What is, then, the peak value of the air-gap flux density? [/FONT][FONT=&quot]Is, then, the assumption about infinite permeability justified?

    Here is the image:


    Any hint concerning any part of this problem will be deeply appreciated. Thanks in advance. :smile:
  2. jcsd
  3. Apr 19, 2008 #2
    Hint 1: How do you model the (coil + core) as a circuit element?

    You haven't shown us your working.

    Assuming this is not a homework question...

    The assumption of infinite permeability does not have to do with resonance, but it helps you proceed and use the circuit model without worrying about nonlinearities in the core. If you meant to ask whether the assumption is valid UNDER resonance, then you have to know more about the material constituting the core and its behavior at different electrical frequencies.

    Hint 2: You already have a capacitance and a resistance. What else do you need in the circuit to achieve resonance? (Extended hint: look at the voltage source...what kind of a source is it?)
  4. Apr 20, 2008 #3
    The source is AC.... I was going to make use of the formula [tex]\omega_0=\frac{1}{\sqrt{LC}}[/tex] for the undamped frequency, but then I'm missing [tex]L[/tex]....
  5. Apr 21, 2008 #4
    Okay, assuming that [tex]\omega_0=f\cdot2\pi[/tex], it looks like the following equality is true: [tex]100\pi=\frac{1}{\sqrt{LC}}[/tex]. But I don't know how to find [tex]C[/tex] (I would, if I knew how to calculate [tex]L[/tex], but I have no idea how from the given information). I'll be really grateful for any hint, it's due in 3 hours......
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