Kirchhoff’s Current Law (KCL) — node balance calculation If 550 mA of current leaves a node and one branch provides 250 mA entering that node, how much current must enter from the other branch to satisfy KCL?

Introduction / Context:
Kirchhoff’s Current Law (KCL) is fundamental for analyzing circuits. It states that the algebraic sum of currents at a node is zero: total entering current equals total leaving current. Applying KCL quickly reveals unknown branch currents and validates measurements.

Given Data / Assumptions:

• Total current leaving the node: 550 mA.
• Known entering current from one branch: 250 mA.
• All currents are steady-state direct currents; directions are defined as entering or leaving the node.

Concept / Approach:
KCL requires Σ I(in) = Σ I(out). If we know the total leaving current and part of the entering current, the remaining entering current is the difference needed to balance the equality.

Step-by-Step Solution:
Write KCL: I_in,total = I_out,total.Given: I_out,total = 550 mA.Known entering branch: 250 mA.Let the unknown entering current be Ix. Then 250 mA + Ix = 550 mA.Solve: Ix = 550 mA − 250 mA = 300 mA.

Verification / Alternative check:
Check balance: entering currents sum to 250 mA + 300 mA = 550 mA, which equals the leaving current; KCL satisfied.

Why Other Options Are Wrong:

• 250 mA: would make total entering 500 mA, not equal to 550 mA.
• 550 mA: would make total entering 800 mA, violating KCL.
• 800 mA: would make entering far exceed leaving; incorrect.

Common Pitfalls:

• Mixing signs and directions; always define “entering” and “leaving” clearly.
• Adding currents without respecting direction, which breaks KCL.

Final Answer:
300 mA