someone help pls

Discussion in 'General Electronics Chat' started by babyboyx, Jun 4, 2009.

  1. babyboyx

    Thread Starter Member

    Jun 2, 2009
    12
    0
    help me pls !!
    how to find the total resistance ??
     
  2. Von

    Active Member

    Oct 29, 2008
    65
    0
    Start by solving the parallel resistances first then simplify until you are forced to solve for parallel again and so on.
     
  3. Zenock

    Active Member

    Jun 1, 2009
    36
    1
    babyboyx --

    If it's R8 that is confusing you. Get rid of it. It doesn't need to be there, it's shorted.

    Now calculate
    \fra{1}{\fra{1}{R4}+\fra{1}{R5}} call it Ra --Parallel Connection calculation

    \fra{1}{\fra{1}{R6}+\fra{1}{R7}} call it Rb --Parallel Connection calculation

    Calculate
    R3+Ra+Rb call it Rc --Series Connection Calculation

    Calculate
    \fra{1}{\fra{1}{R2}+\fra{1}{Rc}} call it Rd -- Parallel Connection Calculation

    Calculate
    R1+Rd call it Rtotal -- Series Connection Calculation

    Z
     
    Last edited: Jun 4, 2009
  4. Zenock

    Active Member

    Jun 1, 2009
    36
    1
    Going forward plug in
    \fra{1}{\fra{1}{R2}+\fra{1}{Rc}} for RD to get...

    R1+\fra{1}{\fra{1}{R2}+\fra{1}{Rc}} Then plug in

    R3+Ra+Rb for Rc to get...

    R1+\fra{1}{\fra{1}{R2}+\fra{1}{R3+Ra+Rb}} then plug in...

    \fra{1}{\fra{1}{R4}+\fra{1}{R5}} for Ra and

    \fra{1}{\fra{1}{R6}+\fra{1}{R7}} for Rb to get...

    R1+\fra{1}{\fra{1}{R2}+\fra{1}{R3+\fra{1}{\fra{1}{R4}+\fra{1}{R5}}+\fra{1}{\fra{1}{R6}+\fra{1}{R7}}}}
     
  5. babyboyx

    Thread Starter Member

    Jun 2, 2009
    12
    0
    ya it really confuse me the R8 ...
    but now thx guys =]
     
  6. babyboyx

    Thread Starter Member

    Jun 2, 2009
    12
    0
    btw if i wanna find the current across R2 need use total current ??
    or just total voltage/R2 ??
     
  7. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    You have to calculate the resistance of the network formed by R4,R5,R6,R7, and R8, lets call it Ra. That resistance is in parallel with R2. Calculate the total resistance of Ra ║R2 , and use that to calculate voltage across R2. Gravy.
     
  8. babyboyx

    Thread Starter Member

    Jun 2, 2009
    12
    0
    mean that i have to use the R2 own voltage right ??
    btw din R3 also parella wif R2 ??
     
  9. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    No, you have to break every problem into it parts and solve all the parts. R2 is in parallel with a bunch of other resistors. Solve the other resistors first, then work on R2 and the other resistors in parallel together, turn them into one resistor. This (║) means parallel to.

    Once you know the voltage across R2 (and the rest) you can solve the problem you're after.
     
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