Quantcast

Got Homework?

Connect with other students for help. It's a free community.

  • across
    MIT Grad Student
    Online now
  • laura*
    Helped 1,000 students
    Online now
  • Hero
    College Math Guru
    Online now

Here's the question you clicked on:

55 members online
  • 0 replying
  • 0 viewing

TomLikesPhysics Group Title

I am supposed to take a hard look at this network, come up with a matrix and use it to get all the currents. Can someone help me to setup the equations for the matrix?

  • one year ago
  • one year ago

  • This Question is Closed
  1. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    This is what I came up with. But according to Wolfram Alpha it can not be solved so I guess my equations to begin with a wrong.

    • one year ago
    1 Attachment
  2. BluFoot Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    Can you rotate the picture please? My neck kinda hurts otherwise :P

    • one year ago
  3. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    o.O Seriously? Every picture is oriented in the right way.

    • one year ago
  4. BluFoot Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    Oh, I'm new sorry. That's a stupid interface. OK I downloaded it... Do you know what A and B are supposed to stand for? voltage sources I guess?

    • one year ago
  5. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    Between A and B we got 10 Volts.

    • one year ago
  6. eSpeX Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    If you set it up using mesh analysis you find that you have two equations and two unknowns. Start with the left mesh and you get: \[R_1i_1 + R_5(i_1-i_2) + R_2i_1 = 0\] and for the right: \[R_4i_2 + R_5(i_2-i_1) + R_3i_2 = 0\] Build your matrix from that.

    • one year ago
  7. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    :O I thought I have 5-6 unknows and as much equations. You did not consider the currents that run into a knot.

    • one year ago
  8. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    Why don´t you got a i4 and i3?

    • one year ago
  9. eSpeX Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    Because there are only two meshes (loops).

    • one year ago
  10. eSpeX Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    Maybe this will help: http://www.allaboutcircuits.com/vol_1/chpt_10/3.html

    • one year ago
  11. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    Yes but that does not mean that the current that runs through r2 is also the current that runs through r4.

    • one year ago
  12. eSpeX Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    Well no, because a mesh is voltage, r*i, so you know the voltage on each of them and thus you can calculate the current through each element.

    • one year ago
  13. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    But we also do not know the voltage on r2 and r4 so we can not say if there runs the same current or not. Why don´t you consider also looking at the knots?

    • one year ago
  14. eSpeX Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    Knots?

    • one year ago
  15. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    A place where the current that goes in equals the current that goes out. The other important part of kirchoffs-rule. Perhaps node is the right word?

    • one year ago
  16. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    The thick dots on the drawing where one line splits into two lines.

    • one year ago
  17. eSpeX Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    Ah, nodes. The nodes are considered. But you know that the voltage drops around any loop equal zero. If you want to do node analysis you would need to know a little more information like the voltage on each side of your circuit or maybe one of the drops within it.

    • one year ago
  18. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    I know the voltage between A and B is 10 Volts.

    • one year ago
  19. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    And through Kirchhoff I know that the currents in a node add up to zero. I used three nodes and two mashes to get five equations. You can see them in the top.

    • one year ago
  20. eSpeX Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    Well you only have two nodes where two or more components meet so that would only yield one equation. Kirchoff's current law says that the current entering a node must equal the current leaving the node, so they do not equal zero.

    • one year ago
  21. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    There are four nodes.

    • one year ago
  22. eSpeX Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    I meant to say, three or more components meet.

    • one year ago
  23. eSpeX Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    However to use node voltage method, you need a reference node as well.

    • one year ago
  24. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    Well know that all the current that goes in has to come out.

    • one year ago
    1 Attachment
  25. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    What do you mean with reference node?

    • one year ago
  26. eSpeX Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    One that equals zero. Although if you took your 'A' side and called it 0, your 'B' as +10, you could do a node equation for the top, and bot nodes. That would give you four equations and four unknowns I believe.

    • one year ago
  27. eSpeX Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    Including the mesh equations.

    • one year ago
  28. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    But if you sum up all the currents equal zero for any node. I don´t need a reference node. Otherwise it would mean that there are electrons pilling up in the node if the sum of all the currents entering and exiting the node does not equal zero.

    • one year ago
  29. eSpeX Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    Perhaps the analysis you are tasked with is using a method that I am unfamiliar with. I am not sure who would be a good person to ask though.

    • one year ago
  30. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    I think I just have to use all of Kirchhoffsrules.

    • one year ago
  31. eSpeX Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    You are going to have 7 unknowns using KCL, with the information you are given it seems to me that using mesh and node analysis would be the easiest way to approach this.

    • one year ago
  32. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    Why do you get 7 unknowns? I get max. 6. We can conclude that I that comes from A into the network is the same I that goes out of the network into B.

    • one year ago
  33. eSpeX Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    Accounting for all of the currents I get 7, if you wish to discount your ib=ia then you would have 6, yes.

    • one year ago
  34. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    Did you solve the system? I threw mine into Wolfram Alpha and got weird stuff, for example i1=i2. That seems very weird to me. Also i4 and i5 are booth negative.

    • one year ago
  35. TomLikesPhysics Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    Can you perhaps help me to calculate the total resistance of this network?

    • one year ago
  36. phi Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    Here is how Prof. Strang would do the problem http://ocw.mit.edu/courses/mathematics/18-085-computational-science-and-engineering-i-fall-2008/video-lectures/lecture-12-graphs-and-networks/ I thought I would apply his approach to your problem.

    • one year ago
    • Attachments:

See more questions >>>

Your question is ready. Sign up for free to start getting answers.

spraguer (Moderator)
5 → View Detailed Profile

is replying to Can someone tell me what button the professor is hitting...

23

  • Teamwork 19 Teammate
  • Problem Solving 19 Hero
  • You have blocked this person.
  • ✔ You're a fan Checking fan status...

Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.

This is the testimonial you wrote.
You haven't written a testimonial for Owlfred.