Spring 2018
Kirchhoff's Laws
Using KCL to find currents through generic elements
Learn It!
Pre-Requisite Knowledge
Goal
Using KCL
Use KCL to find the currents through generic elements in a circuit
Find the values of $I_1$ and $I_2$ in the diagram at left.

$$$a. I_1 = 0.3\text{ A}\text{ and } I_2 = 0.6\text{ A} \\b. I_1 = 0.3\text{ A}\text{ and } I_2 = 0.4\text{ A} \\c. I_1 = 0.4\text{ A}\text{ and } I_2 = 0.4\text{ A} \\d. I_1 = 0.4\text{ A}\text{ and } I_2 = 0.5\text{ A} \\e. I_1 = 0.5\text{ A}\text{ and } I_2 = 0.6\text{ A}$$$
Part 1
Find one unknown current
$\Sigma I_{in}\; =\; \Sigma I_{out}$
KCL is "Kirchhoff's Current Law." It states that the current flowing into a node must be equal to the current that flows out of the node.
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Limits of KCL
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Find KCL equation for one node
$I_2 + 0.1 = 0.5$
KCL expression for node at the bottom of the circuit.
$I_2 = 0.4$
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$I_1 = 0.4 - 0.1 = 0.3$
Substitute $I_2 = 0.4$
$I_1 = 0.3 \text{ A} \text{ and } I_2 = 0.4\text{ A}$