Kirchhoffs LawIn 1845, a German physicist, developed a pair or set of rules or laws which deal with the conservation of current and energy within electrical circuits. These two rules are commonly known as:
Kirchhoffs Current Law, (KCL)
or KCL, states that the “total current or charge entering a junction or node is exactly equal to the charge leaving the node as it has no other place to go except to leave, as no charge is lost within the node“.
In other words the algebraic sum of ALL the currents entering and leaving a node must be equal to zero,
I + I = 0
I2 + I4 + I5 + I6 + I3 + I1 = 0
Kirchhoffs Voltage Law, (KVL)
or KVL, states that “in any closed loop network, the total voltage around the loop is equal to the sum of all the voltage drops within the same loop” which is also equal to zero.
In other words the algebraic sum of all voltages within the loop must be equal to zero.
Sign Convention in Kirchhoff’s Rules:
1. Move through EMF device in assumed direction of polarity (– to +):
e > 0
2. Move through EMF device in opposite direction of polarity (+ to –):
e < 0
3. Move through resistor in assumed direction of current (with current
DV = –IR
4. Move through resistor in opposite direction of current (against current
DV = +IR
5. Move through capacitor from + plate to – plate (with E-field):
DV = –q/C
6. Move through capacitor from – plate to + plate (against E-field):
DV = +q/C