# Mesh eqs

Discussion in 'Homework Help' started by n_adam, Apr 4, 2014.

Mar 1, 2014
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Hi guys,

I need to solve this problem with the mesh current method. I am having trouble figuring out the three equations for the three loops. What confuses me is the current source and that the voltage is unknown across it. Any help or hint would be highly appreciated.

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2. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,393
497
Ok. You did first step. Define the problem.

Next step is to draw mesh currents. Go do that and post a picture.

Mar 1, 2014
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here are the mesh currents

• ###### IMG_0139.jpg
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Mar 1, 2014
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and the three equations I came up with

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5. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,393
497
Ok.

Now. Look at i1. Do you see that i1 enters the current source and exits the current source?

Mar 1, 2014
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Yes, so i1 = 0.01A I assume

7. ### shteii01 AAC Fanatic!

Feb 19, 2010
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497
Yes. i1=10 mA.

However. In the future you have to examine these things carefully. Current has magnitude and direction. In your case the magnitude is 10 mA. We assume clockwise direction of i1 means that i1 is positive. So we look at the direction of the current from the current source, it matches the direction of i1. So i1=10 mA.

However. If direction of current source was opposite of i1, then i1 would have been -10 mA. Meaning that magnitude of i1 is 10 mA, but its assumed direction is wrong which we indicate by the negative sign.

Mar 1, 2014
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Ok thank you I got the right answer.

Mar 1, 2014
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I have an other problem I can't figure out. I am sure I am really close to the solution but something is not right. Would you mind taking a look at what I have so far?

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10. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,393
497
Use mesh current. You have 3 meshes. You will have three mesh currents. The current in left mesh and current in center mesh will have to be solved for. The current in the right mesh is going to the be current of the current source, but watch the direction of the mesh current, the mesh current will point down, the current source current points up, that means mesh current will be -28 A.

Now find the other two mesh currents. Then find the voltages v2 and v3 using Ohm's Law.