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Homework Help: Designing a circuit

  1. Jun 11, 2007 #1
    1. The problem statement, all variables and given/known data
    Choosing from the following resistors values (they may be used more than once), set is, R1, R2, to obtain V = 5.5 V

    [1 kilo ohm, 3.3 kilo ohm, 4.7 kilo ohm, 10 kilo ohm]

    3. The attempt at a solution
    I wasn't actually sure how to attempt this problem my textbook didn't really cover any examples of this. I included the figure needed to solve the problem, just any advice on how to start on it would be great.

    http://img.photobucket.com/albums/v407/dazedoutpinoy/CircuitHomework001.jpg" [Broken]
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Jun 19, 2007 #2
    Use current divider. This problem is more of a trial & error.
    Last edited by a moderator: May 2, 2017
  4. Jun 19, 2007 #3


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    Staff: Mentor

    What is the value of Is? Once you know Is, then you know what R1 // R2 has to be.
  5. Jul 20, 2007 #4
    V = IR

    lol ... um, seriously, you can't really do anything with the values you did give. You would need to know your Vcc I'm guessing and then use a Voltage Divider...The question is way too inexact.
  6. Jul 24, 2007 #5
    Something is wrong with this problem. Are you sure you didn't get a value for [tex]I_s[/tex]? Here's why I'm asking:

    To find V you need:

    [tex]V = IR[/tex]

    Since the circuit you have is parallel, you can rewrite the above equation:

    [tex]V = I_s(\frac{R_1R_2}{R_1 + R_2})[/tex]

    Now re-arranging to solve for I:

    [tex]I_s = \frac{V(R_1 + R_2)}{R_1R_2)}[/tex]

    You have the value of [tex]V[/tex], and plugging in different values of [tex]R_1[/tex] and [tex]R_2[/tex] will simply give you different values of [tex]I_s[/tex], which would all be correct to the values of the resistors.

    So either I'm missing something, or this problem is explained wrong.
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