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

Homework Help: Applications of Linear Systems: Electrical Networks

  1. Feb 6, 2005 #1

    How do I find the current through the central resistor (the one that is 1 ohm) in this Wheatstone bridge attached to this post? What approach do I need to take here if I were to solve this using linear systems? Our professor poorly explained how electrical networks work. I can solve the linear system once I get it but I just need to figure out what I'm supposed to do in order to find those equations. Thanks.

    Attached Files:

  2. jcsd
  3. Feb 6, 2005 #2
    Last edited by a moderator: Apr 21, 2017
  4. Feb 6, 2005 #3
    Try and redraw the circuit, but simplified so it's easier to see all the "routes" the current can go through. That really helps. :smile:
  5. Feb 6, 2005 #4
    Another way, without using the Kirchoff's laws, would consist of using the star-triangle transformations and compute in this way the electric potentials at the ends of the central resistor using only the Ohm's laws.
    Last edited: Feb 6, 2005
  6. Feb 7, 2005 #5
    See that's the thing, he never drew any arrows in the problem. I think he said something like we can make up our own directions but I really couldn't understand him. Would the final answer be the same no matter what the directions were?
  7. Feb 7, 2005 #6
    You can choose your own direction. If you have chosen your arrow in the 'wrong' direction, final answer will reflact that. In other words, you will get a negative result.
  8. Feb 7, 2005 #7
    OK here's a revised drawing of the diagram. I labeled the direction of the current this time. Are these directions fine? I know next to nothing about how current, voltage, and resistance work.

    Attached Files:

  9. Feb 7, 2005 #8
    Now mark the currents with some notations, say I, i, [tex]i_1[/tex].

    Say the current through the battory is I.

    So at the [tex]2 \Omega, 3\Omega[/tex] junction (left side in your recent picture) , let the current through [tex]3\Omega[/tex] is i and current through [tex]2\Omega[/tex] is I-i (Point rule).

    Do similarly at the 3,1,2 junction (top), assuming the current through [tex]1\Omega[/tex] is [tex]i_1[/tex]. Complete the current flow diagram by writing the currents through the other resistors. Don't introduce any other variables.

    You need only three variables namely I, i, [tex]i_1[/tex]. Apply Kirchoff's laws to get three equations to solve.

    Some one will be along with you if there is another easy way to do this.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook