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roam
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Homework Statement
[PLAIN]http://img84.imageshack.us/img84/3711/imagode.gif
Consider the electrical circuit shown above. Using Kirchhoff’s Rules determine the currents I1 and I2.
(Correct answers: I1=-0.727, I2 = 2.33)
The Attempt at a Solution
We can see from the network diagram that there are 3 closed loops, a left inner loop containing a 40 v battery, a right inner loop with a 80 v battery, and an outer loop that contains both batteries. There is also a 60 v battery in the midle that belongs to left and right loops (but not the outer loop).
I'm confused, which (left/right) loop do I need to use for working out I2? each of them gives different results:
Assuming the direction assigned to the loop is counter-clockwise, left loop gives:
[tex]I_2 = \frac{\epsilon_1 + \epsilon 2}{R_1 + R_2} = \frac{100}{115}= 0.86[/tex] which is wrong.
Going around the right loop gives:
[tex]I_2 = \frac{\epsilon_2 + \epsilon_3}{R_2}=\frac{140}{60}=2.33[/tex]
which is the correct answer... but why?
Similarly for finding I1 how do you decide whether you should use the left loop or the big loop? Any guidance is really appreciated.
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