Which statement expresses Kirchhoff's current law for a node?

• A. The sum of voltages around a loop is zero.
• B. The voltage at a node equals the average of neighboring voltages.
• C. The sum of currents entering a node equals the sum leaving.
• D. The current through a branch is constant.

Answer: (C)

At a node, currents must balance because charge can’t accumulate there. Kirchhoff's current law says the total current flowing into the node equals the total current flowing out of the node. In practice, you pick a direction for each branch; treat currents entering as positive, currents leaving as negative, and the sum of all currents at the node must be zero. For example, if two currents enter and one leaves, the entering currents add up to the leaving current (i1 + i2 = i3). If a branch is actually taking current away from the node, its value is negative in this convention, and the equation still holds.

This reflects conservation of charge: whatever current enters the junction must leave it, so there’s no net buildup of charge at the node.

Other statements don’t describe this balance. Saying the sum of voltages around a loop is zero corresponds to Kirchhoff’s voltage law, not current balance at a node. Claiming the voltage at a node is the average of neighboring voltages isn’t a law that governs circuits. Saying a current through a branch is constant ignores how currents depend on the circuit, loads, and sources.