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How to find the voltage 'v' in the given network?

  1. Jul 4, 2015 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations IMG_20150705_074846.JPG


    3. The attempt at a solution
     
  2. jcsd
  3. Jul 4, 2015 #2
    What have you tried?
     
  4. Jul 4, 2015 #3
    i can not able decide which is suitable to find that voltage
    please explain how to find that voltage!
    i am always confused while reducing the network wheather the resistors are in series or in parallel.
    i tried voltage division but getting struck with those resistors can't able to decide they are either in parallel or series
     
  5. Jul 4, 2015 #4
    Write a loop equation around the loop with an open circuit. What does that tell you about V?
     
  6. Jul 4, 2015 #5
    we need voltages across 3 &1ohm resistors for that! How to find those voltages?
     
  7. Jul 4, 2015 #6

    SammyS

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    Don't forget the 6Ω resistor.

    It's a policy at PF, not to give solutions. We are here to help you to arrive at a solution .
     
  8. Jul 4, 2015 #7
    Sir can you please elaborate the explanation on to find that v?
     
  9. Jul 5, 2015 #8
    Write the loop equation around that loop. Just write it in terms of the voltages. Notice that no current flows through the resistor on the top branch. You should get V = something. Your goal is to find out what that something is.
     
  10. Jul 5, 2015 #9

    SammyS

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    Can any current flow through the 1Ω resistor in the circuit as it was presented above?
     
  11. Jul 5, 2015 #10
    no,sir as current requires closed path to flow
     
  12. Jul 5, 2015 #11

    SammyS

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    Then you have a very simple circuit to analyze.
     
  13. Jul 5, 2015 #12
    Sir okay done i found that voltage v=10/3
    now if we want to find the equvalent resistance of that network how to proceed?
    i am getting confused with 1 & 3 Ohm resistors Whether they are in series or parallel?
     
  14. Jul 5, 2015 #13

    SammyS

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    What is the process you are to follow in finding the equivalent resistance?
     
  15. Jul 5, 2015 #14
    Short circuiting voltage source and then to check the resistors whether in series or parallel
     
  16. Jul 5, 2015 #15

    SammyS

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    Right.

    So you must consider all three resistors. What combinations are in parallel ? What combinations are in series?
     
  17. Jul 5, 2015 #16
    I think 3&1 in parallel combination
    this combination is in series with 6 ohm
     
  18. Jul 5, 2015 #17

    SammyS

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    That's not right. Does some of the current flowing through the 1Ω resistor also flow through the 3Ω resistor? Is the voltage drop across these two the same?

    Draw the resulting circuit. You're finding the equivalent resistance from the + terminal to the - terminal with the voltage source shorted.

    Does any pair of resistors have the same current flowing through them?
    Does any pair of resistors have the same voltage drop across them?
     
  19. Jul 5, 2015 #18
    Sir
    total current flowing in the network is 10/9
    because of this currents the voltage drops across the resistors are as follows
    6 ohm is 20/3 Volts
    3 ohm is 10/3 Volts
    but for 1ohm ?????
    i can not able to conclude series and parallel combination reduction it's still confusing me!
     
  20. Jul 5, 2015 #19

    mfb

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    You figured out that no current flows through it. What is the voltage drop at a resistor with a current of 0?
     
  21. Jul 5, 2015 #20

    SammyS

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    That is all for the case in which no current flows through the 1Ω resistor.

    Remember, you were trying to find equivalent resistance with the 10 Volt source shorted out. That means, replace it with a conducting wire. This is one approach to obtaining the solution you want. However, you have not been able to find equivalent resistance this way.

    You haven't actually stated what your ultimate goal way in analyzing this circuit. However, considering that you were looking for the open circuit voltage, and the above equivalent resistance, it's pretty clear that you are looking to find the Thevenin equivalent circuit.

    Apparently you found some current to be 10/9 A. I should ask you how you got that and then wait for your answer, but I need to get to bed.
    (It may purely be a coincidence that these currents are the same, but) 10/9 A is also the current that would flow through the terminals (also through the 1Ω resistor) of the given circuit if you short the resistor terminals. (Edited)

    An alternate way to find the equivalent resistance is to find what resistance is needed with a voltage source of 10/3 V in order to have that current of 10/9 A. Can you find that resistance value?

    Edited
     
    Last edited: Jul 5, 2015
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