Kirchhoff’s First Law − Junction Rule In an electrical circuit, the algebraic sum of the currents meeting at a junction is always zero. I1, I2 I3, and I4 are the currents flowing through the respective wires. Convention: The current flowing towards the junction is taken as positive. The current flowing away from the junction is taken as negative. I3 + (− I1) + (− I2) + (− I4) = 0 This law is based on the law of conservation of charge.
Kirchhoff’s Second Law − Loop Rule In a closed loop, the algebraic sum of the emfs is equal to the algebraic sum of the products of the resistances and the currents flowing through them. For the closed loop BACB: E1 − E2 = I1R1 + I2R2 − I3R3 For the closed loop CADC: E2 = I3R3 + I4R4 + I5R5
This law is based on the law of conservation of energy.