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Serious help needed

  1. Mar 18, 2008 #1
    Hello guys

    Im not good at all with electronics ...... Please help me and please no comments to discourage me.

    I need some help with 2 questions.

    http://www.savefile.com/files/1447466 <-- This file hardly has 3 questions. Please I know they are not long or hard but for me its hard as I have not studied.

    Yes, this is my homework and I do agree that I was not able to go to my classes. Therefore im struggling.

    Please help !!!
    Atleast with some questions if not all.

    Thank You
     

    Attached Files:

    • Help.doc
      Help.doc
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    Last edited: Mar 18, 2008
  2. jcsd
  3. Mar 18, 2008 #2
    the link has the doc file with the question. It has a diagram in it.

    I cant just copy paste the diagram here. Otherwise diagram will get messey. Please look at the doc file.

    Thank You
     
  4. Mar 18, 2008 #3
    For your comfort I have attached the file in here. Please help now.
     

    Attached Files:

    • Help.doc
      Help.doc
      File size:
      290.7 KB
      Views:
      40
  5. Mar 19, 2008 #4
    For the first one, its asking that you use branch current analysis, this means they want you to use KCL (Kirchhoff's current law). A good way to figure out the currents into each node is to circle every node you see. If multiple components appear on the same node, draw a circle around the "super" node by circling all of the components' terminals on that "super" node together. This can help to simplify how you see the circuit. Label each node as an unknown voltage (Va, Vb, Vc, etc. and one can be a reference 0 node like ground). Draw current arrows into and out of each node and label them as well, and remember KCL while drawing these currents. Next, list all of the unknown currents and voltages (some maybe have the same node as you labeled already) that you either need to solve for or that you don't know and may need anyway to arrive at the final answer. From that point you just keep writing all of the obvious equations that you can of the circuit you're analyzing while including these unknown voltages and currents until you have enough equations to solve for all of the unknowns. Finally, remember KCL, and use it to solve for the currents at each node. KCL is used to generate a lot of your equations.

    For the second problem it is asking to use a source transformation. The key concept behind this is to understand Norton's theorem and Thevenin's theorem. Remember a norton source (current source in parallel with a load) is equivalent to a thevenin source (a voltage in series with a load). To make the equivalence, you use ohm's law to determine the voltage or current. You can see the circuit given shows a CURRENT source (norton's theorem) so you want to turn it into an equivalent voltage source (thevenin). From there you have a bunch of resistor's in series, and you just use your voltage divider rule to solve for the voltage across the resistor with the unknown voltage. Likewise, you can use the current divider rule which gives you the currents through a dividing network. It may help you to lump the resistor's in series and knowing KCL, you can determine that the current through the lump is equal to the current through the single resistor in question. With the last part you need to make use of parallel and series resistor rules to simplify the group of resistors into an equivalent single resistance. From there you use the same ideas from the previous parts.

    for question 3, do like question 1. Write down your unknown voltages and currents, and then write down every possible equation of KVL (one for every loop you see) and of KCL (circle your nodes and write down equations for all of the currents through components that are between 2 nodes).

    I use to think I could do this stuff at the last minute too after skipping a lot of classes cause it seemed easy, but honestly you can't skip classes (more importantly skip homework) and expect to learn this type of material easily. I had to drop the course and start over because I thought I just had to know the equations and laws and easy examples, and then the test came and there were circuits with 12 loops, 4 different dependent and independent sources, and all other kinds of crazy stuff in a single circuit problem, and it is overwhelming unless you get LOTS of practice doing these problems. When I retook it, I spent my time on the homework and ended up with an A. There are definitely tricks and strategies that you're not taught by equations and laws to solve a lot of these circuit analysis problems, and unless you have an hour to spend on each problem there is no way you will figure the strategies out to solve them. So I must suggest you spend a lot of time on these problems, and then practice more and more if it isn't too late.
     
    Last edited: Mar 19, 2008
  6. Mar 19, 2008 #5
    thanx a lot mate. Unfortunately you were a bit late :( I had handed in my assign I have no idea what I did in it. Hopefully, I'll pass in that.

    Thank You again.
     
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