Series-Parallel circuit

Discussion in 'Homework Help' started by tjjam2003, Apr 5, 2006.

  1. tjjam2003

    tjjam2003 Thread Starter Member

    Joined:
    Apr 5, 2006
    Messages:
    22
    In a Series-Parallel circuit, how do you find the resistance and the current if only the voltage is given? 5 resistors in series and 1 resistor in parallel.

    R1= 3 ohm Voltage= 3V Current 1A
    R2= 5 ohm Voltage =1.65 current 0.33A

    R3= ??? voltage= 4 volts (parellel)

    R4= 4 ohm Voltage 1.32 Current 0.33
    R5= 1 ohm voltage 1 volt current 1A
    R6=3ohm voltage 0.99 current 0.33
  2. windoze killa

    windoze killa Distinguished Member

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    Feb 23, 2006
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    Melbourne Australia
    Could you draw the circuit please. What you have here doesn't seem to make sense.

    If all these resistors that are in series are really in series then the current through them all will be the same. If R1 and R2 are in series you can't have 1A through one and .33A through the other.
  3. rodn.m

    rodn.m Member

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    May 3, 2006
    Messages:
    12
    hi, if you are adding resistors in series
    Rt=R1+R2+R3
    For resistors in parallel
    Rt=R1*R2/R1+R2
    to add more than 2 resistors in parallel
    do above calc for R1 and R2
    Then do same calc for above result and R3
    then simply add total series and parallel resistor values together.
  4. radiosmoke

    radiosmoke Member

    Joined:
    May 30, 2006
    Messages:
    17
    ------------------------------
    All current that goes into a circuit must leave the same circuit.

    (since you have 3 resistors that have .33a they must be in series.)

    R2 + R4 + R6 so 5ohms + 4ohms +3ohms = 12ohms

    Rt1 = 12
    It1 = .33amps
    Et1 = Rt1 X It1 or 12 X .33 = 3.96v (I will round that to 4v)
    ---------------------------
    and

    two resistors have 1 amp of current flowing they must also be in series.

    Rt2 = R1 + R5 or 3ohms + 1 ohm = 4ohms

    so

    E2t = It2 X Rt2 or 4ohms X 1 amp = 4volts
    ------------------------------------------
    Since both have a total of 4 volts across the series branches
    both of these series circuits are in parallel

    Then add the R3 with a 4volt drop also to the circuit, and since its in parallel, it uses E = I X R

    or 4V = 1amp X 1ohm, Since the 4volts is across the resistance of R3 it must be 4ohms and a current of 1 amp.
    ohms law proves this R =E / I or 4v / 1 amp = 4 volts

    ----------------------
    To continue:
    you have a series parallel circuit (that is actually three series circuits, that are in parallel
    -------------
    Just for fun:
    Adding the currents and using ohms law, we see that
    Rt = Et / It or 4v / 2.33 amps = 1.73 ohms of Total resistance.


    This is a close approximation of the total resistance of the circuit.
    ---------
    There are other methods that may work also, but, I find this the most logical, without going into higher math, (which I abhor)
    -----
    Hope this comes close to the answer your looking for.
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