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something about mesh analysis confuses me and I can't find an explainaton anywhere, as you can see on this picture (it's in French, but the schema and formulas should be enough to understand)

enter image description here

They bascially explain how mesh analysis works, and that's fine and all, I understand the formulas but then I get this exercise :

enter image description here

And as you can see they just put I2 = -2A. Why do we not care about the 12 and 3 resistances ? The exercise is basically the same as the image shown above and in that one we take both R2 and R3 into account.

Is it because this time we have a current source ? Or because we are on the "edge" on the circuit ?

Thanks for reading and thanks in advance to those who will answer

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  • \$\begingroup\$ There is an excellent video on Youtube by Mathtutor explaining the process, that attempting to replicate the way he explained it would be an insult to them. I will let you judge for yourself. Mesh current in circuit analysis \$\endgroup\$
    – AlanZ2223
    Dec 28 '14 at 18:33
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It's because of the current source and the fact that I2 is the only mesh current in that branch. I2 can't be anything other than -2 amps, so you don't need to write a loop equation for it.

If you swap the current source and the 12 ohm resistor, then you get an extra equation (I2 - I1 = 2 amps) and an extra unknown (the voltage across the current source).

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