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Homework Help: A few circuit analysis questions.

  1. Oct 17, 2004 #1
    hey guys
    i posted this in the electrical engineering section
    but realised this may have been a better place to
    post since i am studying this in university :-)
    hello there,
    i'm wondering how to go about solving this problem
    A diagram of the circuit can be seen here
    http://www.compsoc.nuigalway.ie/~filter/images/circuit.gif [Broken]
    (i threw it together in microcap) the pulse sourse is actually
    meant to be a 2Amp current source. the capacitor
    has a value of 1micro-Farad.

    By using superposition i have to find the steady state DC
    current flowing in the 20 Ohm resistor. i could usually do
    this easy but the capacitor is throwing me off. im assuming
    that once a steady state has been reached, the capacitor
    will be fully charged and no current will actually be flowing
    into it right? if this is the case.. i decided that i could ignore
    its effects.. because it should really have any. and this
    appears to work. i dont know if its a fluke or not though.

    the answers are 0.4A flows in the 20 Ohm resistor due to
    the current source and 0.1A flows in the 20 Ohm resistor
    due to the voltage source.

    any ideas on how to go about this would be welcome.

    i need my mind to be put at rest :-) cheers, Nik
    Last edited by a moderator: May 1, 2017
  2. jcsd
  3. Oct 17, 2004 #2


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  4. Oct 17, 2004 #3
    thanks very much!
    one thing though..
    how did you come to the conclusion that there is 10V across the capacitor?

  5. Oct 17, 2004 #4
    yes i know that, but where did the extra 5 volts come from?
  6. Oct 18, 2004 #5


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    From the voltage across the 10 ohm resistor connected in series with the voltage source. There is 0.5 A current flowing through it, and it produces 5 V across it, according to Ohm's law. This adds to the 5 V of the voltage source.
    And the 0.5 A current through the 20 ohm resistor produces 10 V and it is connected to the terminals of the capacitor. The current through the other 10 ohm resistor is 1 A, it also produces 10 V.
    Those 10 ohm and 20 ohm resistors are connected parallel with each other, and with the capacitor, too. The same voltage has to be across all of them.

    Last edited: Oct 18, 2004
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