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Electronics (Circuit Analysis) Questions

  1. Jan 20, 2014 #1
    1. The problem statement, all variables and given/known data

    Problem A
    http://imagizer.imageshack.us/v2/800x600q90/855/6v0c.png [Broken]

    Problem B
    http://imagizer.imageshack.us/v2/800x600q90/853/1m2c.png [Broken]
    http://imagizer.imageshack.us/v2/800x600q90/34/wfe4.png [Broken]

    2. Relevant equations

    Kirchhoff's Rules/Ohm's Law

    Voltage Divider Formula

    [tex] V_{ab} = (V_{0}*R_{2})/(R_{1} + R_{2}) [/tex]

    3. The attempt at a solution

    Problem A:

    I'm unsure how much information is sufficient for what the question is asking. I derived these equations, and relations for different currents:

    [tex]I_{1} = I_{AB}=I_{EF}[/tex]
    [tex]I_{3} = I_{BC}=I_{CD} = I_{DE} [/tex]
    [tex]I_{2}=I_{BE}[/tex]

    Loop 1 (Clockwise)
    [tex] 0 = V_{0} - I_{1}R - I_{2}R - I_{1}R = V_{0} - 2I_{1}R - I_{2}R [/tex]

    Loop 2 (Clockwise)
    [tex] 0=V_{0} - 1/2 V_{0} - I_{3}R \ \mbox{(used Voltage Divider Eq for the voltage of GH)} [/tex]
    [tex] \Rightarrow 0 = V_{0} - 2I_{3}R [/tex]

    Node Equation

    [tex] 0 = I_{1} - I_{3} - I_{2} [/tex]

    Solving these equations I get

    [tex] 3 I_{1} = I_{3} [/tex]
    [tex] I_{2} = -2 I_{1} [/tex]
    [tex] I_{3} = - (3/2) I_{2} [/tex]

    So for the questions asked:

    a.) V_{GH} = V_{0}/2
    b.) I_{GH} = V_{0}/2R
    c.) I'm not sure how to find this.


    Problem B:


    V Thevenin is equal to V_{GH} right? That means V_{th} = V_{GH} = V_{0}/2

    R Thevenin is R parallel to R, which can be found with 1/R_{th} = 1/R + 1/R which give us R_{th} = 2/R.

    I'm not as confident of Problem B as I am of Problem A.
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Jan 20, 2014 #2

    berkeman

    User Avatar

    Staff: Mentor

    This problem is easiest to solve by using series & parallel combinations of resistors.

    For a), collapse the circuit from right to left, combining resistors as you go. You will end up with only one resistor -- this tells you the overall current from the voltage supply. Then re-build the original circuit from left to right, calculating currents and voltages as you go.
     
  4. Jan 20, 2014 #3

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    1. In problem 13, did you get something like V_be = V_o/3 ?
    If so, don't you think V_gh = Vo/2 is a little strange ?
    I do not understand your 1/2 V_o in loop 2.
     
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