Which statement defines Kirchhoff's current law?

• A. KCL states the sum of voltages at a node equals zero.
• B. KCL states the sum of currents entering a node equals the sum leaving.
• C. KCL states the product of currents at a node is zero.
• D. KCL states total circuit current is constant regardless of node.

Answer: (B)

Kirchhoff's current law says that at a junction, the total current flowing into the node must equal the total current flowing out. This reflects the conservation of electric charge: charge can't accumulate at a point, so all currents into the node must be accounted for by currents leaving it. When you write it, you can treat currents entering as positive and leaving as negative, and the algebraic sum at the node equals zero. This is why, for example, if two currents enter a node and one leaves, the leaving current must equal the sum of the entering currents. The other statements mix in voltages, claim a product of currents is zero, or suggest the total circuit current stays the same at every node, which aren’t descriptions of Kirchhoff's current law.