What is Kirchhoff’s laws?
Kirchhoff’s laws are more comprehensive than ohm’s law and are used for solving
electrical networks.
The two Kirchhoff’s laws are:
1. Kirchhoff’s Current Law (KCL)
2. Kirchhoff’s Voltage Law (KVL)
Kirchhoff’s Current Law (KCL)
It states that “the algebraic sum of the currents in a junction of a circuit is zero.
(or)
The sum of current entering the junction is equal to the sum of the current leaving
the junction.
Explanation:
Consider 5 conductors carrying currents. Assume positive sign for the current flowing
towards the junction and negative sign for the current flowing away from the junction.
Let P is a junction
I1, I3, & I4 = incoming current towards the junction P
I2, & I5 = outgoing current away from the junction P
By applying Kirchhoff ’ s current law at junction P,
I1 - I2 + I3 + I4 - I5 = 0
I1 + I3 + I4 = I2 + I5
Sum of incoming current = sum of outgoing
current
Kirchhoff’s Voltage Law (KVL):
It states that in any closed electrical circuit, “the algebraic sum of voltage is zero”.
(OR)
That is the sum of voltage rises (EMF) in a closed network is equal to the sum of
voltages drops (P.D)
Explanation:
Consider a simple closed electrical circuit,
Let,
E - Supply voltage
R1, R2 & R3 - Resistors in the circuit.
I - Current flow through the circuit
V1 – p.d across R1
V2 – p.d across R2
V3 – p.d across R3
Applying Kirchhoff’s voltage law to the closed circuit,
E - V1 - V2 - V3 = 0
E = V1+V2+V3 ----------- (1)
Substitute, V1 = I.R1, V2 = I.R2 & V3 = I.R3 in equation (1)
E = IR1+IR2+IR3
E - IR1 - IR2 - IR3 = 0 [Algebraic sum of voltages is zero]
