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Series and parallel circuits

  1. Jun 16, 2009 #1
    1.Find the equivalent resistance seen by the source and use the result to find i, i sub1, and v.

    the equivalent resistance i got is 8 ohms
    my value for i is 6A
    and my value for i sub1 is 1A
    my v is 40V,,

    are my answers correct?? help.. im quite unsure of these..
     

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    Last edited: Jun 16, 2009
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  3. Jun 16, 2009 #2

    LowlyPion

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    Not quite. Your equivalent resistance is correct. That's the good news.

    But the Ii through the smaller of the parallel resistors would be bigger than the I2 of the larger resistor wouldn't it? I think you have the currents reversed. Namely that the current divides 5:1 alright, but the 5 goes through the smaller R, and the 1 through the larger.

    Also, you know that the current is 6A from the power source. The voltage drop across the first R then will be 3*6 = 18V. That means that the voltage on the other side of the 3Ω is going to be 18V less than 48 or 30V, not 40 as you have written.
     
  4. Jun 16, 2009 #3
    does that mean that the value of v is 30V?
    if that's the case, what would be the voltage on the resistor that has 6 ohms?

    Or should the voltage of the 6 ohms and 30 ohms resistor be the same? Because its already parallel.. am i right?
     
  5. Jun 16, 2009 #4

    ideasrule

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    "Or should the voltage of the 6 ohms and 30 ohms resistor be the same? Because its already parallel.. am i right?"

    Absolutely. Resistors in parallel have the same voltage across them.
     
  6. Jun 16, 2009 #5

    LowlyPion

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    They are in parallel to the same nodes. And that node is at 30V. So ... yes the same voltage across both.

    30V/6 = 5A and 30A/30 = 1 ... 5 + 1 = 6

    The current's right. The voltages are right.

    Alessandro Volta, Gustav Kirchhoff and Georg Ohm are all happy, even if all dead.
     
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