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Current circuit

  1. Jul 9, 2011 #1
    1. The problem statement, all variables and given/known data

    I want so show that U1=U*R2/(R1+R2) (sorry latex didn't work for me right now, don't know why)



    2. Relevant equations



    3. The attempt at a solution

    I know the solution but I don't understand one step:
    The solution says the following: the fall of voltage at U1 = R2*I (I is the current which comes from U). Why is that? Thats doesn't make sense to me, because I thought the current "splits" at this spot so I have: I=I1+I2.
    Why does the solution say it's U=R2*I


    Thanks for the help
     

    Attached Files:

  2. jcsd
  3. Jul 9, 2011 #2
    well u is the emf of the source right ?
    but what is this ---------u1 ? wat's U1
     
  4. Jul 9, 2011 #3
    I don't know how to describe it properly in english, but I think it's the voltage which drains off. I think the english term is voltage divider. But as I'am writing this I think I oversaw something.
    The resistances are in series so the current is everywhere the same. Is this the right solution for the problem?
     
  5. Jul 9, 2011 #4

    I like Serena

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    Homework Helper

    That's because the current does not really split.
    The point where U1 is measured is not attached to anything, so no current flows.

    This is indeed *only* a voltage divider.
    Of course, when something (significant) is attached, the currents and voltages will change.
     
  6. Jul 9, 2011 #5
    Ok, I didn't recognize that I have to handle it this way. Thanks for the help
     
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