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Circuit to change the current and voltage of a dc circuit?

  1. Jan 25, 2015 #1
    I wasn't sure whether to post this here or in the 'homework' section... technically it is not a homework question, but I will be happy to move it...

    I am really struggling with this circuit:
    upload_2015-1-25_14-16-29.png
    :'(
    At the moment, I have no clue what to do for part i). I am sure that I will get part ii) afterwards, but I just don't know how to change the pd and current, and I don't really understand the purpose of the 0V terminals..

    Thank you in advance for any help!
     
  2. jcsd
  3. Jan 25, 2015 #2

    Baluncore

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    This question seems to be context related.
    It will be testing the coursework just done, so we need to know what that was and what questions came earlier.
     
  4. Jan 25, 2015 #3

    Stephen Tashi

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    Have you been studying "two port" networks or was this question asked before that topic was mentioned ?

    You could look at examples of two port networks that have voltage sources in them to get some ideas.
    There are lots of notes about two port networks online. e.g. http://ocw.nthu.edu.tw/ocw/upload/12/237/05handout.pdf
     
  5. Jan 25, 2015 #4

    jim hardy

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    Have you studied Thevenin and Norton yet?

    If so you know the answer already and just need the courage to risk making a mistake or two.

    Always parse questions to break them into individual parts.
    False starts are just experiments . You have to go down a lot of blind alleys to learn any neighbvorhood...

    What's simplest two element circuit you can think of that containss a voltage(p.d.) and resistance ?
    Now - if we take them at their word and give Iin a small constant value,
    i think you can answer (i) with one component.

    That should lead you into answer for (ii).
     
  6. Jan 25, 2015 #5

    Baluncore

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    This question comes from olympiad past papers, Page 3, so there is no history to help identify "very simple crcuit".
    http://www.physics.ox.ac.uk/olympiad/Downloads/PastPapers/BPhO_Round_2_Paper_2012_Final.pdf

    The question may be deliberately vague so as to see how students handle the challenge. The simplest circuit that I can see is Vin through a voltage follower with a series resistor, R, to Vout. There may be no right answer.
     
  7. Jan 25, 2015 #6

    jim hardy

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    Interesting set of questions.

    Vin and Iin are irrelevant
    (i) is a voltage source of Vout in series with r, or a current source of Vout/r in parallel with r.

    (ii) is worded to trip up those who do not read carefully. It mixes constant current and voltage sources, to make it hard for beginners.
     
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