Hong Kong Institute of Vocational Education (Morrison Hill)
Department of Real Estate and Facilities Management
Electrical Theory Laboratory Sheet: BSE3424/LA03
Student name: ________________________ Course/Year: __________ Date: _________
Kirchhoff’s Voltage and Current Laws
Objectives
•
•
•
•
To prove the current I are linearly proportional to the voltage V in a dc circuit.
To show that this proportional constant is equal to the resistance R of the circuit.
To verify Kirchhoff’s voltage law (KVL).
To verify Kirchhoff’s current law (KCL).
Apparatus
• Digital Multimeter (DMM) X 2
• dc power supply
• proto board
Components
• Resistors: 1.2kΩ, 1.8kΩ, 2.4kΩ, 3.3kΩ, 4.7kΩ, 5.6kΩ, 6.8kΩ, 8.2kΩ
BSE3424/LA03
Updated on 01/2007
Page 1 of 5
PART A: BACKGROUND
Kirchhoff’s Voltage Law states that the algebraic sum of voltages around a closed loop is
equal to zero. With regard to the following diagram, this means that
VS - V1 -V2 -V3 -V4 = 0
or
VS = V1 + V2 + V3 + V4
R2
R1
I
+ V1 -
+
VS
-
+ V2 R3
+
V3
+
V4
-
R4
By connecting such a circuit and measuring the voltages, it should be possible to verify this
relationship.
Kirchhoff’s Current Law states that the sum of the currents into a junction is equal to the
sum of currents out of that junction. With reference to the following diagram, this implies
that
IT = I1 + I2 + I3 + I4
or
IT + I1 + I2 + I3 +I4 = 0
IT
+
VS
-
I1
I2
I3
R1
R2
R3
I4
R4
If you connect up this circuit, you should be able to verify this rule by measuring each of the
currents.
BSE3424/LA03
Updated on 01/2007
Page 2 of 5
PART B: PROCEDURES
B1
Kirchhoff’s Voltage Law
A
R1
I1
B
I2
+ V1 -
R2
+ V2 -
I4
+
VS
-
C
I3
+
V4
-
+
V5
-
R4
I6
R3
I5
F
E
D
Figure B1
1.
Select any four resistors from the eight resistors supplied, measure their individual
resistance, and record in Table 1.
Table 1
R1
R2
R3
R4
Measured Resistance
values
2.
Using the proto board to connect the four resistors as shown in Figure B1. Assume a
supply voltage Vs of 10V and measure the voltage across each resistor by a voltmeter.
Record the results in Table 2.
Table2
V1
V2
V3
V4
Measured voltage
values
In each of the following closed loops determine the resultant loop voltage (following
a clockwise direction and taking the polarity of individual voltage into consideration):
ABEF: _____________________________________________________________
BCDE: _____________________________________________________________
ACDF: _____________________________________________________________
BSE3424/LA03
Updated on 01/2007
Page 3 of 5
B2
Kirchhoff’s Current Law
1.
Using the same circuit in Figure B1, connect an ammeter in series with the resistors
R1, R2, R3, R4, one by one to obtain the current flowing through them and record the
results in Table 3.
Table 3
I1
I2
I3
I4
Measured current
values
2.
Calculate the total current at the following junctions by assuming the current flowing
into a junction is positive and the current flowing out from a junction is negative
Junction B: __________________________________________________________
Junction C: __________________________________________________________
Junction E: __________________________________________________________
3.
Using the measured voltage across and current through each resistor, and by Ohm's
Low, calculate the resistor value of R1, R2, R3, R4, and record the calculated results
in Table 4.
Table 4
R1
R2
R3
R4
Calculated resistance
values
BSE3424/LA03
Updated on 01/2007
Page 4 of 5
PART C: DISCUSSIONS
1.
What is the conclusion that you can draw from calculating the closed loop voltage?
____________________________________________________________________
2.
What is the conclusion that you can draw from calculating the total junction current?
____________________________________________________________________
3.
Is there any difference between the readings in Table 1 and Table 4? Why?
___________________________________________________________________
___________________________________________________________________
BSE3424/LA03
Updated on 01/2007
Page 5 of 5