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Homework Help: Calculating the current supplied battery, working out P.D...

  1. Nov 17, 2015 #1
    1. The problem statement, all variables and given/known data
    2. Relevant equations
    Ohms Law
    R-total = R1 X R2/(R1+R2)
    Potential difference (V) = current (I) x resistance (R).
    3. The attempt at a solution

    a) Can complete on my own.

    b) Really no clue tbh, I would assume it revolves around ohms law but I'm not sure how it fits in here.

    c) I believe I can just use Potential difference (V) = current (I) x resistance (R). so
    3 x 0.04 = 0.12 .

    d) Clueless but would assume there is a formula which revolves around parallel resistors.
  2. jcsd
  3. Nov 17, 2015 #2


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    What is the p.d. across X? You have answered c. Put that in your diagram and see what it tells you.
  4. Nov 17, 2015 #3
    I'm not sure how to work out P.D without knowing the resistance?
  5. Nov 17, 2015 #4


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    For b) you need one of Kirchhoff's circuit laws. In each node the sum of the entering and leaving currents must be zero. Within a continuous cable without node the current must be constant. Try to apply this law to the nodes of your circuit.

    c) is correct

    For d): In c) you just calculated the potential difference at resistor Y. As the cables are supposed to be without resistance, what does that mean for the potential difference at the battery as well as for the resistor X?
  6. Nov 17, 2015 #5
    for D does it mean they also have 0.12V? and then
    Resistance = Voltage ÷ Current
    0.12 ÷ 2 = 0.06
  7. Nov 17, 2015 #6


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    Yes, it does. If the resistance of the cables is zero the potential difference in the cables ΔU = Rcable ⋅ I + 0 ⋅ I = 0. I didn't see your drawing, but I just guess how it looks like and claim: All the cables above the resistors and the battery must have the same voltage, as well as all the cables below.
  8. Nov 18, 2015 #7
    Use this logic
    When there is a circuit of parallel:
    V is same across all resistance . So ultimately current will vary with resistance.
    Total current = current across resistor 1 + current across resistor 2
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