Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Node-voltage Method, some misconception?

  1. May 5, 2012 #1
    Node-voltage Method, some misconception??

    Please check the attachment:
    The question is written upon it

    Sorry bad drawing, the circuit is closed from the left hand side but not from the right hand side.
     

    Attached Files:

    Last edited: May 5, 2012
  2. jcsd
  3. May 5, 2012 #2
    Re: Node-voltage Method, some misconception??

    But I don't see any problem. We can choose any node we want as a reference point (GND).
     
  4. May 5, 2012 #3
    Re: Node-voltage Method, some misconception??

    But the essential node must connect at least 3 appliances!! Here we have only two :/
     
  5. May 5, 2012 #4
    Re: Node-voltage Method, some misconception??

    But you can solve the circuit using nodal analysis without any "essential node".
    And I still don't understand why you need "essential nodes"?
     
  6. May 6, 2012 #5
    Re: Node-voltage Method, some misconception??

    What's nodal analysis? How does it differ from node-voltage method. Elaborate please.
    [I only learnt node-voltage method :p]
    If we are talking only node-voltage method, how in the world did the Doctor consider the node below a reference when it only connects two appliances[see figure].
    That's my question.
     
    Last edited: May 6, 2012
  7. May 6, 2012 #6
    Re: Node-voltage Method, some misconception??

    I just checked, and they mean the same. Yet again, this is against the rule.
     
    Last edited: May 6, 2012
  8. May 6, 2012 #7
    Re: Node-voltage Method, some misconception??

    Nodal analysis is exactly the same think as node-voltage method.
    And we can choose any node we want as a reference point (GND).

    See the example

    attachment.php?attachmentid=47008&stc=1&d=1336291275.png

    We have a four nodes in our circuit. I pick as a reference point (GND) node 4.
    So node 4 by de definition has a potential of 0 V.
    So we left with three nodes. but we know that voltage at node 1 is equal 9V.
    So we only has two unknown nodal voltages 2 and 3.
    Now we apply KCL to the nodes where the unknown voltages appears.

    For node 2 (I assume that all current flow out from the node)

    [tex]\frac{V2}{R2} + \frac{V2 - V1}{R1} + \frac{V2 - V3}{R3} = 0 [/tex]

    And we notice that V1 = E1 = 10V

    Now we write KCL for node 3.

    [tex]\frac{V3 - V2}{R3} + \frac{V3 - V1}{R4} = 0 [/tex]

    And now all we have to do is to solve for V2 and V3

    http://www.wolframalpha.com/input/?i=A/3+++(A+-+9)/9+++(A+-+B)/9+=0,+(B-A)/9+++(B+-+9)/9=0

    V2 = 3V and V3 = Vth = 6V
     

    Attached Files:

  9. May 6, 2012 #8
    Re: Node-voltage Method, some misconception??

    Lots of thanks Jhony, now I get it..
     
  10. May 6, 2012 #9
    Re: Node-voltage Method, some misconception??

    We always measure all the voltage respect to this common point (reference point), also known as a "ground" (GND). And we assume that GND have zero voltage.
    Look ta this examples

    attachment.php?attachmentid=47009&stc=1&d=1336293980.png

    attachment.php?attachmentid=42873&d=1327068105.jpg
     

    Attached Files:

    • 0.1.PNG
      0.1.PNG
      File size:
      7.6 KB
      Views:
      330
  11. May 6, 2012 #10
    Re: Node-voltage Method, some misconception??

    Thanks, that's very kind of you.
    You really were helpful
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Node-voltage Method, some misconception?
  1. Node Voltage Analysis (Replies: 3)

Loading...