İzmir University of Economics
EEE 205 Fundamentals of Electrical Circuits Lab
EXPERIMENT 4
Kirchoff's Voltage Law
A. Background
As introduced in Experiment 3, the German physicist Gustav Robert Kirchhoff
stated two rules regarding the behaviour of electrical circuits. The first rule,
known as Kirchhoff’s Current Law (KCL), is about the currents entering and
exiting a node.
The second rule is known as Kichhoff’s Volage Law (KVL). KVL states that “the
sum of the source and voltage voltages around any closed path in a circuit is
equal to zero”. Consider the circuit given in Fig. 4.1.
+ v1 -
+ v2 -
vS
IS
+
v0
-
Fig.4.1.
The KVL expression around the closed loop is that:
+ v1 + v2 + v0 – vs = 0
Voltage Division Formula:
Consider the resistive circuitry given in Fig.4.2.
I
+ V1 -
+ V2 -
R1
R2
R3
VS
+
V3
-
Fig.4.2.
The KVL equation around the closed path (loop or mesh) yields
4-1
V1 + V2 – V3 - Vs = 0
or
Vs = V1 + V2 – V3 - Vs
i.e., the sum of the voltage drops over the resistors are equal to the voltage
source applied.
Assume a current I flows arounf the loop. Then
V1 = R1 I
V2 = R2 I
and
V3 = R3 I
Subtituting these into the KVL equation we get
Vs = R1 I + R2 I + R3 I = (R1 + R2 + R3) I
or
I=
1
R1 +R2 +R3
V
Then
V =
V =
R1
R1 +R2 +R3
R2
R1 +R2 +R3
V
V
and
V =
R
R1 +R2 +R3
V
Above results indicate that the voltage Vs applied to the circuit is divided
between the resistors in accordance with their resistance values.
4-2
B. Preliminary Work
Consider the circuit given in Fig. 4.3.
I
VS
10 V
+ V1 -
a
+ V2 -
1.2
Ω
+
1.8 kΩ
Va
1 kΩ
+
V3
-
Fig.4.3.
1. Determine the current I.
2. Determine the voltages V1, V2 and V3.
3. Determine the node voltage Va.
4. Relate the voltage Va to V1, V2 and V3.
4-3
C. Experimental Work
1. Attach the Y-0016/001 modul on your experiment set and make the circuit
connections as given in Fig. 4.4.
E
Fig 4.4
2. Apply the voltages given below to your circuit respectively and measure
the voltage values for every step. Write your measurements onto the
Table 4.1.
Table 4.1.
E (Volts)
(adjusted)
E (V)
(Measured)
V1 (V)
V2 (V)
V3 (V)
V1+V2+V3 (V)
2
4
6
8
10
3. Is Kirchhoff Voltage Law verified at evey step? Is KVL dependent on the
input voltage applied?
4-4