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Homework Help: How to find currents and voltages in circuits

  1. Mar 16, 2005 #1
    I have to find the Requivalent and all of the currents and voltages in the circuit below.

    l------------Resistor 1----l---------l
    l l l
    battery l l
    l Resistor 2 Resistor 3
    l l l
    l l l

    My picture is not showing up right, so I'll try to describe it. The battery is on the left and the wire moves up to the right where resistor 1 is. The wire continues, but splits into two paths (making a parallel). The wire turns to the right, where resistor 2 is, but if you keep going straight and then turn right, thats where resistor 3 is.

    they give us the following:
    R1=40 ohms
    R2=60 ohms
    R3=60 ohms
    Vtotal=120 V

    I am not sure where to even start. I know V=IR, and I-V/R, but I don't know how to find the other numbers. I also know that in a series, current stays the same while voltage changes, while in parallel, current changes, while voltage stays the same.

    I also know that for series, the Req= R1+R2, while in a parallel, 1/Req=1/R1+1/R2

    I just can't figure out the numbers when you have a parallel in a series. Can you help me get started?
    Last edited: Mar 16, 2005
  2. jcsd
  3. Mar 16, 2005 #2
    The two resistors that are in parallel are equivilent to a resisitor with the resistance of R where (1/R)= (1/60)+(1/60) which would be 30 ohms and then that equivilent resistor is in series with the first resistor so dont you just add them together so the total resistance would be 70 ohms?
  4. Mar 16, 2005 #3


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    I agree with Yapper .. By your description, it sounds like R2 & R3 are in parallel, so 60ohm || 60ohm = 30 ohms. The 30ohms is then in series with R1. So Req = R1 + R2 || R3

    Do you know how to determine all the currents and voltages in your circuit, from here?
  5. Mar 17, 2005 #4
    No, I don't. Could you explain it to me?
  6. Mar 17, 2005 #5
    Could you creat a drawing in paint, so the image would be easier to work with? That way, you might receive more help.
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