Circuit analysis nodal

Discussion in 'Homework Help' started by yiannistamv, Jul 24, 2014.

  1. yiannistamv

    Thread Starter Member

    Jul 23, 2014
    35
    0
    can someone also explain to me why this (see photo) thanks you
     
    • 1.jpg
      1.jpg
      File size:
      70.9 KB
      Views:
      26
  2. anhnha

    Active Member

    Apr 19, 2012
    774
    48
    The voltage at the top node of 5V voltage source is 5V (with ground reference). So, the current through the 2 ohms resistor
    i1 = (v1 - 5)/2.
    Similarly, the voltage at the top node of 3V is -3V (with ground reference). So, the current through the 4 ohms resistor
    i3 = (v1 - (-3V))/4 = (v1 + 3)/4.
     
    yiannistamv likes this.
  3. yiannistamv

    Thread Starter Member

    Jul 23, 2014
    35
    0
    please let me know if the current vector was towards the node (i mean know kircoff equation is -i1+i2-i3=0 if it was i1+i2-i3=0) then it would be the same or not? thank you
     
  4. anhnha

    Active Member

    Apr 19, 2012
    774
    48
    Sorry, I am not sure if I understand your question.

    [​IMG]


    If all current directions are reverse as shown in the picture, then the Kirchhoff's Current Law for the top node is i1 + i2 + i3 = 0. However, i1, i2 and i3 now will be a bit different.
    See the picture.

    BTW, you can choose the current in any direction you want but after that you need to express in in terms of node voltage correctly and the result should be same for v1.
     
    • KCL.PNG
      KCL.PNG
      File size:
      75.7 KB
      Views:
      48
    yiannistamv likes this.
  5. anhnha

    Active Member

    Apr 19, 2012
    774
    48
    Here is another way:

    [​IMG]
     
  6. yiannistamv

    Thread Starter Member

    Jul 23, 2014
    35
    0
    i can not thank you enought thank you
     
Loading...