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Using the junction shown in the figure, which equation correctly applies Kirchhoff's Current Law? 
A$I_1+I_2+I_3=I_4+I_5+I_6$
B$I_1+I_4=I_2+I_3+I_5+I_6$
C$I_1+I_2+I_4=I_3+I_5+I_6$
D$I_1+I_2+I_3+I_4+I_5+I_6=0$
Answer & Solution
Correct answer: A. $I_1+I_2+I_3=I_4+I_5+I_6$
The figure shows $I_1$, $I_2$, and $I_3$ entering the node and $I_4$, $I_5$, and $I_6$ leaving it. Kirchhoff's Current Law requires entering current to equal leaving current, giving $I_1+I_2+I_3=I_4+I_5+I_6$. Option D would only be valid if signs were assigned algebraically, not as all positive magnitudes.