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Homework Help: Batteries connected in parallel and resistance

  1. Oct 16, 2007 #1
    1. The problem statement, all variables and given/known data
    What i may ask may seem simple, but it is casuing me a lot of headaches. What is the effective potential difference across a resistor if it is connected to a parrallel connection of batteries. Lets quantify the variables. Battery one has an e.m.f. of 2 V while battery 2 has an e.m.f. of 6V. Resistor has a resistance of 7ohms.

    2. Relevant equations
    Kirchoff's spotential difference law

    3. The attempt at a solution
    Ok, according to kirchoff's second law, for any closed loop, the algebraic sum of potential difference is 0. But for both closed loops, the potential difference across the resistor is different. So what really happens in this case? Will the potential difference across the resistor be 5V and the 2V battery does not release a current at all? Please help. Surely this is not the case.
  2. jcsd
  3. Oct 16, 2007 #2


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    Staff Emeritus
    Science Advisor

    The lower potential battery is something of a short circuit across the higher potential battery, so some energy (current) from the higher potential battery flows to the lower one. Both batteries would have some internal resistance (usually low).
  4. Oct 16, 2007 #3


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    Homework Helper

    note the problem here is that you have connect two supposedly ideal voltage source in parallel 6V vs 2V, each will try to maintain a different voltage at the common terminal! that means normal ideal circuit analysis assumptions cannot be applied for your circuit is inconsistent (it is like saying terminal AB must be 6V and 2V simultaneously which cannot happen in a classical world). That is why you are getting a contradiction when applying your rules.
  5. Oct 16, 2007 #4
    Hmm so what really happends if we were to set up such a connection in reality? What assumptions of an ideal battery might be compromised?
  6. Oct 16, 2007 #5
    I wouldn't advise you to try this. In first semester we learned to never connect batteries of different voltages in parallel. the result will be bad.

    Batteries of equal potential must be carefully considered for this as they should be exactly the same. They will produce half the current each to the resistor.
  7. Jun 25, 2011 #6
    if i connect 1.5 v battery of internal resistance 0.5 ohm in parallel with 1.2 v cell of 0.7 ohm internal resistance what will happen?
    and if i connect whole ckt to the infinity load than what would be the power diliverd by the battery?
  8. Jun 26, 2011 #7
    What kind of result can we expect. Can it happen that the batteries will also be charged/discharged in such a manner that both of them have same potential.
  9. Jun 26, 2011 #8
    i have one exercise about it and i dont know how to calculatwe pls tell me calculation
  10. Jun 26, 2011 #9


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    Staff: Mentor

    Draw the resulting circuit (be sure to include the battery internal resistances). Apply Kirchhoff's and Ohms laws to analyze it.
  11. Jan 21, 2012 #10
    Define voltage & current batteries in parallel
    V= increase I= same
    In series what ?
  12. Jan 21, 2012 #11
    Identical natures of battery
    in series the emf varies at load as increase in voltage & current remain same
    the polarity tune as +to - Or -to +

    in parallel case it is consider to batt of same range in voltage & internal registance
    in this case amp increase but voltage remains same
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