Kirchhoff’s Laws — A/L Physics

Kirchhoff’s Current Law (KCL) The algebraic sum of currents entering a junction equals the algebraic sum of currents leaving that junction. At any node in a circuit, charge cannot accumulate; therefore, the total current flowing in must equal the total current flowing out. This is a direct consequence of conservation of charge. For example, at a junction where three wires meet, if 2 A enters from one branch and 1 A from another, then 3 A must leave through the third branch.

Kirchhoff’s Voltage Law (KVL) The algebraic sum of all potential differences (voltage rises and drops) around any closed loop is zero. This follows from conservation of energy: as you travel around a closed path, the net change in electric potential must be zero. In a simple battery-resistor loop, the voltage rise across the battery equals the sum of voltage drops across the resistors. For instance, in a loop with a 12 V battery and two resistors, the sum of the resistor voltages must be 12 V.