Im getting two solutions using CW and CCW mesh currents?

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Vohms

Joined Feb 3, 2015
1
Hi, I am new here and I am currently learning Thevenin. Can someone please explain why I get two solutions if I use either Clock-Wise or Counter-Clock-Wise. I thought it did not matter which way you chose, but for this problem I am getting two sets of answers. I used KCL and KVL and they both check out. So what am I dong wrong. Here is the circuit.
upload_2015-2-3_18-44-31.png

Here are my equations after trying to solve for Thevenin and assuming no current goes through the a and b wires.

CCW
100i + 5000i2 - 7i = 0
i - i
2 = 100/1000

CW

100i + 7i + 5000i2 = 0
-i +i
2 = 100/1000


When I solve these currents I get different solutions. i2(5000) = ?
 

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t_n_k

Joined Mar 6, 2009
5,448
You need to pay much closer attention to your signs. I believe both CCW & CW loop forms have sign errors.
 

WBahn

Joined Mar 31, 2012
24,693
You say that you got two different answers. I don't see any answers at all! How can we tell you whether your answer(s) is(are) right or wrong if you don't tell us what you got? We are NOT mind readers!

When you say that they both check out, what do you mean? That when you take your solutions and plug them back into the ORIGINAL circuit, that they both satisfy the circuit constraints? That's how you check your solution. You do NOT just plug the numbers back into the equations that produced them because all that shows is that you solved those equations successfully, NOT that the equations themselves have any bearing to the problem being solved.

In looking over your equations, I see a sign error in the CW equation set. I think your CCW ones are correct.
 
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