Problem

Discussion in 'General Electronics Chat' started by Annu007, Nov 16, 2006.

  1. Annu007

    Thread Starter Member

    Jun 12, 2006
    11
    0
    Hello,
    Can anybody show me how to solve this problem (Value of R2)?
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    Best solution for me is using Kirchhoff´s law:
    1) Sum of currents in one joint equals 0
    2) Sum of voltages in one loop (don´t know the right term) is equal to zero.

    Look at www.allaboutcircuits.com for explanation
     
  3. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
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  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Once you have reviewed the material contained in the link that Dave has posted, then give the calculation a whirl and then post your calculations and your results. We will be happy to provide you a bit of guidance if needed.

    hgmjr
     
  5. Annu007

    Thread Starter Member

    Jun 12, 2006
    11
    0
    I came up with 13K for R2.
    Vo = 0.25ma * 5K +0.7V
    Vo = 1.95V
    I1= I2 + ID
    I1 = 12V/30K =0.4mA
    ID = 0.25mA (Given)
    I2 = 0.4-0.25 =0.15mA
    V0 = 1.95V
    R2 = 1.95V/0.15mA = 13K
     
  6. richbrune

    Senior Member

    Oct 28, 2005
    106
    0
    The part about 12v/30k doesn't look right; the voltage drop across the 30k can't be all of the 12v, it's got to be something less than that, seems like about 9 or 10 volts, because you've got to subtract the voltage drops caused by all of the 3 remaining components. I got 40678, but I don't have time to check it before I leave---Sorry, Rich
     
  7. Annu007

    Thread Starter Member

    Jun 12, 2006
    11
    0
    Vo = 12-1.95 = 10.05V

    I1 = 10.05/30K = .335mA

    I2 = 0.335-.25 = .85mA

    R2 = 1.95/0.85 = 22.94K
     
  8. Syed

    New Member

    Dec 5, 2005
    6
    0
    Right..... except 0.335-0.25=0.085 and 1.95/0.85=2.2941 so 1.95/0.085=22.941
     
  9. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Not a bad effort, annu007.

    I used Millman's Theorem and arrived as 22.941K....

    hgmjr
     
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