# badly need to solve this problem plzz

Discussion in 'Homework Help' started by Rezwana Hossain, Oct 18, 2013.

1. ### Rezwana Hossain Thread Starter New Member

Oct 18, 2013
4
0
T.2 Find the current through I 4Ω
resistor using Y − Δ or YΔ − transformation
technique only for the circuit shown in fig below

I found the circuit current using the transformation having problem finding I through 4Ω resistor pleasehelp.

2. ### WBahn Moderator

Mar 31, 2012
20,226
5,749
Why do you badly need to solve this problem?

What you do badly need to do is show YOU effort to solve YOUR homework problem. That way we have a starting point to work from and guide you along from there.

3. ### Rezwana Hossain Thread Starter New Member

Oct 18, 2013
4
0
sry I didn't get you.

4. ### Ramussons Active Member

May 3, 2013
623
104
Explain how you found the circuit current.
What transformation did you do?

Ramesh

5. ### WBahn Moderator

Mar 31, 2012
20,226
5,749
Let me be more explicit: SHOW YOUR WORK!

6. ### WBahn Moderator

Mar 31, 2012
20,226
5,749
As you decide which transformations to do, you have lots of options. Since you are looking for a particular current, let that be your guide in doing your transformations by picking transformations that will maintain the integrity of the information you eventually want. Ideally this would mean keeping that particular resistor in the circuit as you simplify things around it. If that isn't possible, then you want to either maintain the integrity of the nodes on either side of it or of the current path through it. The nature of delta-wye transformations makes doing the latter very difficult, but the former is pretty straightforward. So label the nodes (always a good practice) and then choose transformations that keep the nodes on either side of the target resistor intact. This largely amounts to never doing a wye-delta transform in which one of those nodes is the center of the wye. But it also means never combining two resistors that are in series if one of those nodes is the center node.

By doing things this way, as soon as you get a circuit that you can solve for the voltages at those two nodes, you are done. Because all that is left is to apply the difference between those two node voltages across the original resistor and you have the current (magnitude and direction) through that resistor.

7. ### Rezwana Hossain Thread Starter New Member

Oct 18, 2013
4
0

I have solved this using delta wye transformation and found the current

8. ### WBahn Moderator

Mar 31, 2012
20,226
5,749
Are you sure?

Notice that you are claiming that the current in the target resistor (the 4Ω resistor in the original schematic) is the same as the total current in the supply. Do you believe this?

You've violated the itegrity constraints I was talking about.

In the original circuit, the 4Ω resistor is between Node C and Node E (you really should provide a diagram showing the original circuit with the node labels you've assigned). In each step of your transformation, you need to make sure that you keep those two nodes intact and present.

Notice that the current in the 2Ω resistor in your final diagram is NOT the current that is in the original 4Ω resistor. This can be seen by looking at the very first transformation. The current in the new 2Ω resistor has to be the sum of the actual currents in the 4Ω and in the 6Ω resistors.

You've definitely got the right idea and you are very close to getting it solved.

9. ### Rezwana Hossain Thread Starter New Member

Oct 18, 2013
4
0
I said in my 1st post that I found total circuit current (which I've showed) and I was having problem finding current through 4Ω.

I knew that current flowing through 4Ω is not the total current its simple.

one asked to know how I used delta wye transformation and found total ckt current so that's why I showed my work.

is this called violation??? then I'm sorry.
but thanks for the response.

10. ### WBahn Moderator

Mar 31, 2012
20,226
5,749
Ah, I thought you were saying that you had figured out how to solve the entire problem as opposed to showing how you got to where you presently are. My apologies.

The "violation" I was refering to are the steps in the approach I described about four posts back.