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Homework Help: Change in voltage due to additional source

  1. Dec 31, 2014 #1
    1. The problem statement, all variables and given/known data

    A voltage source connected to a circuit produces a voltage V, current I and has internal resistance R. What is the new voltage if an identical voltage source is added to the original:

    a) in parallel
    b) in series

    2. Relevant equations


    3. The attempt at a solution

    a. For a voltage source in parallel, the equivalent resistance is R/2. Each source provides a current I so the total current is I+I=2I. Therefore the new voltage is V_n=(2I)(R/2)=IR=V unchanged

    b. The equivalent resistance is 2R and the current is I because they are in series, so the new voltage is V_n=I(2R)=2V doubled.
  2. jcsd
  3. Dec 31, 2014 #2


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    Did you have any further questions?
  4. Dec 31, 2014 #3


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    Staff: Mentor

    What is the effect of the circuit to which the voltage supplies are connected? Presumably the voltage mentioned is meant to be the voltage across that load?


    When you connect an identical source in parallel with the first, I agree that the effective internal resistance is halved while the effective cell voltage remains the same. But how will that effect the voltage V that is measured across the load resistance?
  5. Jan 1, 2015 #4


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    The original question is badly worded. I suppose you had better assume the load is resistive.
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