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For the junction shown, if $I_1$, $I_2$, and $I_3$ are all increased by the same amount while $I_4$ and $I_5$ remain unchanged, what happens to $I_6$? 
AIt decreases by the same amount
BIt increases by three times that amount
CIt remains unchanged
DIt becomes zero
Answer & Solution
Correct answer: B. It increases by three times that amount
Using KCL, $I_6=(I_1+I_2+I_3)-(I_4+I_5)$. If each of $I_1$, $I_2$, and $I_3$ increases by an amount $\Delta I$, the total entering current increases by $3\Delta I$. Since $I_4$ and $I_5$ stay fixed, $I_6$ must increase by $3\Delta I$.