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Find the Thevenin resistance for network with dependent current source

  1. Feb 20, 2013 #1
    1. The problem statement, all variables and given/known data


    http://imageshack.us/a/img15/7218/sg2prob11.jpg [Broken]



    Find the Thevenin resistance for the network


    (Sorry for the bad drawing, but that is a point like point / node A on the bottom where it's going out too and likely part of the load too, with a wire connected to the circuit, I'll see if I can draw it better when I get home)

    2. Relevant equations

    V = IR

    KVL, KCL,

    voltage division, current division

    Thevenin procedures, etc

    3. The attempt at a solution

    I'm not sure how to approach this problem, because of that dependent current source (49i). Apparently you can't just silence the voltage source and then take the resistance from point a to the bottom point (which would've just been 96.7 ohms).

    Any tips?
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Feb 20, 2013 #2

    The Electrician

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    Re: Find the Thevenin resistance for network with dependent current so

    Where is the current i defined?
     
  4. Feb 20, 2013 #3
    Re: Find the Thevenin resistance for network with dependent current so

    I'm not too sure about that either, but it would probably have to do with the non-load in the circuit?


    Or can you take that dependent current source as part of the load too? Or just cut it out of the wire (open-circuited) ?? (Where I guess the current i would then be in the rest of the circuit)
     
    Last edited: Feb 20, 2013
  5. Feb 20, 2013 #4

    The Electrician

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    Re: Find the Thevenin resistance for network with dependent current so

    Apparently the dependent current source generates a current of 49 times i, where i is a current somewhere else in the network. i could be the current in either of the resistors, for example. You need to find out where i is.
     
  6. Feb 20, 2013 #5
    Re: Find the Thevenin resistance for network with dependent current so

    Once you figure out where the current for the dependent source is defined in the circuit the rest of the problem should be pretty straight forward.

    To find find the Thevenin resistance looking into the terminals you must first find the open circuit voltage and the short circuit current.
     
  7. Feb 20, 2013 #6
    Re: Find the Thevenin resistance for network with dependent current so

    So is it possible to find an 'I' or is it impossible without an 'I' specifically given.

    (My professor wrote up this problem and it's possible he forgot to put this on the problem and he's done it before)
     
  8. Feb 20, 2013 #7

    The Electrician

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    Re: Find the Thevenin resistance for network with dependent current so

    You can't solve the problem with knowing what current is represented by "i".
     
  9. Feb 21, 2013 #8
    Re: Find the Thevenin resistance for network with dependent current so

    He gave the answer to R(Th) though, would it be possible to solve for I then?
     
  10. Feb 22, 2013 #9

    The Electrician

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    Re: Find the Thevenin resistance for network with dependent current so

    What did he give? Did he also give Vth? It would probably be possible to work the problem with all possible locations for i and see which one gave the Rth you prof gave you.
     
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