Which expression represents Kirchhoff's current law at a junction?

Which expression represents Kirchhoff's current law at a junction?

• A. Sum of voltages around a closed loop equals zero
• B. Sum of currents into a junction equals the sum of currents out
• C. Product of currents around a closed loop equals zero
• D. The sum of currents in a single branch is zero

Answer: (B)

At a junction, charge cannot accumulate in steady state, so the current flowing into the node must equal the current flowing out. This balance is Kirchhoff's current law: the sum of currents into a junction equals the sum of currents leaving the junction. It embodies conservation of charge in circuits. The alternative about voltages around a closed loop is Kirchhoff's voltage law, which is a different statement about energy changes rather than current balance. The idea of a product of currents around a loop isn’t a valid circuit law. And the notion that the sum of currents in a single branch is zero is not correct, since a branch can carry nonzero current and KCL applies specifically at nodes where currents meet.

At a junction, charge cannot accumulate in steady state, so the current flowing into the node must equal the current flowing out. This balance is Kirchhoff's current law: the sum of currents into a junction equals the sum of currents leaving the junction. It embodies conservation of charge in circuits.

The alternative about voltages around a closed loop is Kirchhoff's voltage law, which is a different statement about energy changes rather than current balance. The idea of a product of currents around a loop isn’t a valid circuit law. And the notion that the sum of currents in a single branch is zero is not correct, since a branch can carry nonzero current and KCL applies specifically at nodes where currents meet.