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Heat loss in a circuit

  1. Jul 1, 2017 #1
    1. The problem statement, all variables and given/known data
    Determine the heat loss in the circuit that is connected in series with two batteries (12 V and 6V) and two resistors (6ohms and 4 ohms).

    2. Relevant equations


    3. The attempt at a solution
    I used the difference in P = V^2/R, the power dissipated in the circuit, to calculate the heat loss.
    Heat energy loss/t = (12^2/6) - (6^2/4) = 15W.
    Apparently, I am incorrect; but I don't know the right direction to solve this problem.
    Thanks in advance for your guidance/help.
     
  2. jcsd
  3. Jul 1, 2017 #2
    What is the total voltage change across the batteries? What is the total resistance of the resistors? What is the current?
     
  4. Jul 1, 2017 #3

    gneill

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    Staff: Mentor

    How did you decide that there was 12 V across the 6 Ω resistor and 6 V across the 4 Ω resistor? What is the current flowing in the series circuit? Can it be different for different components? Try writing KVL for the loop.
     
  5. Jul 1, 2017 #4
    See you used the formula , P=V^2/R but as you mentioned the resistors are connected in series. The formula you used was when the resistors are connected in parallel. Thus wrong formula= wrong answer

    Now don't just abuse . Say the right formula. I think most of the people would have this ridiculous thought in their mind . Try using the formula -
    P=I^2Rt
    Hope it helped!
     
  6. Jul 2, 2017 #5

    CWatters

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    Science Advisor
    Homework Helper

    The equation P=V^2/R works just fine for ALL circuits (series or parallel) if you use the correct values for V and R.

    See post #3
     
  7. Jul 2, 2017 #6

    phinds

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    Gold Member
    2016 Award

    draw a circuit diagram and show your calculations for the loop current and how you arrive at it and derive the power from it
     
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