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PinguZaide

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Hello everyone. Hope somebody can help.

We are given the following circuit.

http://puu.sh/70uaQ.png

We need to find the currents i1, i2 and i3 by explicitly using the mesh law.

There are no relevant equations.

So, I draw these 4 meshes on the circuit.

Let's call iA the current in mesh A, iB the current in mesh B, and so on.

Let's also call v_I0 the voltage at I0 and v_I1 the voltage at I1. For each current source, we assume the current enters at + and leaves at -.

Considering we already know the current in mesh D, there is no need to build an equation for that one. We only need to build the equations for meshes A, B and C.

We know that iD = 4A and that iC - iA = 2A, so that iC = 2 + iA.

I ended up with those equations.

12 = 2 * (iA) + 2 * (iA - iB) - v_I0

-6 = 2 * (iB - 4) + 2 * (iB - iA) + 2 * iB

24 = 1 * iC + v_I0 + 1 * (iC - 4)

After some algebra, and by substituing iC = 2 + iA, we end up with 3 equations and 3 unknowns in iA, iB and v_I0.

I end up finding iA = 6.875A, iB = 2.625A and v_I0 = 10.25V, so iC = 8.875.

Therefore, the currents that we want to know are :

i1 = iA = 6.875A

i2 = iA - iB = 4.25A

i3 = iD = 4A

The problem I have is that I used an online tool called DoCircuits to simulate the circuit, and by the result of the run, I would be suppose to have :

i1 = -4.375A, i2 = 5.25A and i3 = 4A

(Link to the circuit : http://www.docircuits.com/my-circuit/7691/2)

I therefore think there must be something I did wrong...

Thanks to anyone who helps me. :)

## Homework Statement

We are given the following circuit.

http://puu.sh/70uaQ.png

We need to find the currents i1, i2 and i3 by explicitly using the mesh law.

## Homework Equations

There are no relevant equations.

## The Attempt at a Solution

So, I draw these 4 meshes on the circuit.

Let's call iA the current in mesh A, iB the current in mesh B, and so on.

Let's also call v_I0 the voltage at I0 and v_I1 the voltage at I1. For each current source, we assume the current enters at + and leaves at -.

Considering we already know the current in mesh D, there is no need to build an equation for that one. We only need to build the equations for meshes A, B and C.

We know that iD = 4A and that iC - iA = 2A, so that iC = 2 + iA.

I ended up with those equations.

__Mesh A__12 = 2 * (iA) + 2 * (iA - iB) - v_I0

__Mesh B__-6 = 2 * (iB - 4) + 2 * (iB - iA) + 2 * iB

__Mesh C__24 = 1 * iC + v_I0 + 1 * (iC - 4)

After some algebra, and by substituing iC = 2 + iA, we end up with 3 equations and 3 unknowns in iA, iB and v_I0.

I end up finding iA = 6.875A, iB = 2.625A and v_I0 = 10.25V, so iC = 8.875.

Therefore, the currents that we want to know are :

i1 = iA = 6.875A

i2 = iA - iB = 4.25A

i3 = iD = 4A

The problem I have is that I used an online tool called DoCircuits to simulate the circuit, and by the result of the run, I would be suppose to have :

i1 = -4.375A, i2 = 5.25A and i3 = 4A

(Link to the circuit : http://www.docircuits.com/my-circuit/7691/2)

I therefore think there must be something I did wrong...

Thanks to anyone who helps me. :)

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