Kirchhoff's Current Law

Kirchhoff's Current Law (KCL)

The sum of all currents that enter an electrical circuit junction is 0. When the currents enter the junction have positive sign and the current that leave the junction have negative sign:

Σ ( Entering Currents) = Σ ( Leaving Currents)

KVL example

V_S = 12V, V_R1 = -4V, V_R2 = -3V

V_R3 = ?

Solution:

∑V_k = V_S + V_R1 + V_R2 + V_R3 = 0

V_R3 = -V_S  - V_R1 - V_R2 = -12V+4V+3V = -5V

The voltage sign (+/-) is the direction of the potential difference.