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Total Resistance of circuit, when there is current source

Discussion in 'Electronics Homework Help' started by A155S, Nov 25, 2014.

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  1. A155S

    A155S

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    Nov 25, 2014
    Ive attached image of a circuit.

    Ignoring the open circuit at the end, how would you calculate the total resistance? Do you just ignore the current source and do it as if it were not there?
     

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  2. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    No the addition of the current source modifies the current and causes less current in the circuit. So although you have the same physical resistors which would give you the same resistance, the addition of the current source effectively increases the resistance of the whole circuit thus reducing the total current.
    Adam
     
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    What do you mean "the total resistance"? There are several ways that question could be interpreted.
     
  4. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    I thought the same Kris. I guess they mean effective resistance including the effect of the current source. But that's just a guess.
    Adam
     
  5. Laplace

    Laplace

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    Apr 4, 2010
    Is there any possible logical reason why the problem would be asking for something other than the Norton or Thevenin equivalent resistance? Maybe just to confuse the student?
     
    Arouse1973 likes this.
  6. Gryd3

    Gryd3

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    Jun 25, 2014
    I'm not sure I have the required skills to answer this... but what is the reference?

    Total resistance as seen by the battery, the constant current source, or the terminals on the right (as the open circuit).
    Would this not completely change the answer?
     
  7. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    I am guessing it is as Laplace stated, the equivalent resistance that would be seen by the battery? I know I said effective, I think equivalent is a better word.
    Adam
     
  8. Laplace

    Laplace

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    Apr 4, 2010
    The question of the reference was answered when the problem provided the open terminals. There is no logical reason to assume the problem means anything else than the equivalent resistance at the open terminals. Of course, if the problem actually stated something else then I would go with that.
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    My guess is that it's asking for the impedance of the device when used as a power supply.

    But yeah, since we're all coming up with different guesses it certainly suggests that the problem needs to be clarified.
     
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  10. Laplace

    Laplace

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    Apr 4, 2010
    But to answer the OP's question, the internal resistance of a current source is infinite so for the purpose of calculating circuit resistance (whatever that may mean) the current source is replaced by ∞Ω.
     
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