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Homework Help: EMF/ circuit question

  1. Mar 9, 2010 #1
    1. The problem statement, all variables and given/known data
    If R1 = 4 x R2 then what are the values of the potential difference in terms of the EMF, E?
    s.png
    I have R1 = 3/4, and R2 = 1/4 but that seems a bit simplistic, then I tried plugging it into equations and got completely different answers.

    2. Relevant equations
    R=V/I (?)
    EMF=v1 +v2


    3. The attempt at a solution
    First I simply put it as 1/4 and 3/4, then I plugged it into the equations:
    v=IR
    v1=1(4) =4
    v2=1(1) =1
    EMF=v1 + v2 = 5
    R2 = 1.25, R1 = 5

    ??
     
  2. jcsd
  3. Mar 9, 2010 #2

    collinsmark

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    Homework Helper
    Gold Member

    Solve the current, I. Express this interim result as a function of E, R1 and R2.

    Since you know that R1 = 4 x R2, you can now express the current solely as function of E and R2 (since R1 goes away after the substitution).

    Now that you know the current, using V = IR, find the EMF (i.e. voltage) across R2. You should be able to express it solely as a function of E (after some algebraic simplification).
     
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