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Homework Help: Batteries in circuit, terminal voltage

  1. Jun 12, 2008 #1
    1. The problem statement, all variables and given/known data

    two batteries are connected as shown, see attached 'drawing.' what is the terminal voltage across each battery

    2. Relevant equations

    electric potential V = IR where I is current, R is resistance

    I = V_0/R * e^(-t/RC) where t is time, C is capacitance <--RC circuit, discharging (10V batt.)

    I = dQ/dt where t is time, Q is charge

    I = epsilon/R e^(-t/RC) where epsilon is emf <---RC circuit, charging (5V battery)

    3. The attempt at a solution

    i am not too sure about how to approach the problem but by looking at the drawing, i am making the assumption that the current follows a counterclockwise path and that the 10V battery is discharging -->doing work on the 5V battery?

    is my assumption correct, if not, how should i approach the problem?

    help appreciated

    Attached Files:

    • batt.JPG
      File size:
      10.3 KB
  2. jcsd
  3. Jun 12, 2008 #2


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    Homework Helper

    Hi scholio,

    There are no capacitors here, so the equations with capacitances do not apply. You only need Ohm's law, but you might want to solve it using Kirchoff's equations.

    The current will not be going counterclockwise. If the 10 V battery was the only battery, the current would be going clockwise. If the 5 V battery were the only battery, it would be going counterclockwise. Since they are both there and the 10V battery has a larger voltage, the current is clockwise.

    I don't think you need to account for any discharging or charging of the batteries. Just treat this as a normal circuit. Find an expression for the current, then find the potential difference between the terminals of the batteries (which means, for the left battery, the potential difference from the bottom of the resistor to the top of the 10V emf source).
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