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Circuit with capacitors and inductors

  1. Mar 19, 2012 #1
    2r2cbh5.png
    The question states that the circuit has been connected for a very long time. I'm assuming that then, the current will remain constant and thus the voltage for the inductor is vL = Ldi/dt = 0. Thus, using nodal analysis, I was able to solve (a) by eliminating all of the inductors from the circuit. For (b), however, there is a capacitor for which I do not know how to handle, although I would guess that a mesh analysis would be involved from the looks of the current sources.
     
  2. jcsd
  3. Mar 19, 2012 #2

    gneill

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    Staff: Mentor

    When capacitors reach steady state in a DC circuit they reach a constant voltage and pass no current. You can remove capacitors and short out inductors...
     
  4. Mar 19, 2012 #3
    I have removed the capacitors and shorted out the inductors. All that remains are the resistors. Would it be valid to sum the current sources and put the 12 A source to the left of everything and use current division?
     
  5. Mar 19, 2012 #4

    gneill

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    No, you can't sum the current sources as they are not in parallel. But you don't need to: the 10A supply is the only supply to the 2k and 5k resistors which are in parallel (now that the inductor is shorted). Apply current division.
     
  6. Mar 19, 2012 #5
    Why doesn't the 2 A source have no added effect? I would assume from intuition that it would contribute to the current i,x going through the 5 k,ohm resistor.
     
    Last edited: Mar 19, 2012
  7. Mar 19, 2012 #6

    gneill

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    The 2A source can't have any effect on those components because the 10A current source will pass 10 amps, and ONLY 10 amps no matter what. An ideal source cannot do anything but exactly what it's specified to do. If an ideal source is putting 10A into a node, you better believe that all 10A are going somewhere! :smile:

    If you were to draw a current arrow on the bottom rail that is below the 10A source, what current value would you label it with? Where does that current come from ?
     
  8. Mar 20, 2012 #7
    10 A going to the left?
     
  9. Mar 21, 2012 #8

    gneill

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    Yes. Where does that current come from (through which components must it flow)?
     
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