Cant get voltage drop!!

Discussion in 'Homework Help' started by emagdnim47, Mar 7, 2013.

  1. emagdnim47

    Thread Starter New Member

    Jul 16, 2011
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    0
    This problem is seeking us to find the missing values below. I got pretty far in it up until I hit the unknown voltage drop values. Why do I get voltage drops that are higher than the applied voltage by x2 or x3 in value?!?! I went back many times to check my IT as well as RT. It all checks out, maybe I'm completely helpless.....PLEASE HELP!

    ***My work and the circuit diagram is attached to this thread in pdf format, thank you in advance for your guidance!


    Unit 8: Practice Problems# 2 and 4 (page 223)

    2) Find the unknown values in the circuit if the applied voltage is 350 V and the resistors have the following values:
    R1= 22k Ω, R2= 18k Ω, R3= 12k Ω, R4= 30k Ω

    IT= E1= E2= E3= E4=

    RT= I1= I2= I3= I4=
     
    Last edited: Mar 7, 2013
  2. WBahn

    Moderator

    Mar 31, 2012
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    Your first expression (make it an equation!) implies that R1 is in parallel with R4 and that both are in parallel with the series combination of R2 and R3. Look at the circuit. Are R1 and R4 in parallel?
     
  3. emagdnim47

    Thread Starter New Member

    Jul 16, 2011
    21
    0

    I've got a bad habit of doing that, I'll make corrections:)

    Oh my! I should change the equation then:

    Rreq= R2 x R3/R2 + R3?

    Then take the R1 & R4 values, and add them together to get RT since they're (series) components?

    Alex
     
  4. Jony130

    AAC Fanatic!

    Feb 17, 2009
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  5. WBahn

    Moderator

    Mar 31, 2012
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    You are being sloppy with your math. By order of operations, what you have written is:

    Rreq= [(R2 x R3)/R2] + R3?

    You need to review what it means for components to be in parallel and in series.

    Two (or more) components are in series if the same current that flows through one of them has to flow through all of them.

    Two (or more) components are in parallel if the same voltage that appears across one of them has to appear across all of them.

    In your case, there are only two components that meet one of these descriptions, namely R2 and R3. They are in series. So replace them with a single equivalent resistance called R23. The new diagram will show that you still have just two components that meet one of these descriptions, namely R4 and R23, but they are in parallel. So replace them with a single equivalent resistance called R234. The new diagram will show that the remaining two resistors, R1 and R234, are in series. Replace them with a single resistance called R1234 or just Req or Rt.
     
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