Experiment 1
Kirchhoff’s Laws
Kirchhoff’s current law (KCL) states that the algebraic sum of the currents entering any
node in a circuit is equal to zero. Kirchhoff’s voltage law (KVL) states that the algebraic sum of
the voltages around any closed path in a circuit is equal to zero. This experiment will verify
these laws.
Kirchhoff’s current law will be verified by measuring the current flowing through each of
the four branches of a circuit as shown in Figure 1. One of these branches is a voltage source,
the other three are resistors. The digital ammeter measures the current flowing through the meter
from the red input terminal to the black output terminal. In order to measure the current through
any branch, it is necessary to insert the
ammeter in series with the branch. This is
done at the points labeled J1, J2, J3, and J4,
being careful to maintain the red meter
terminal connection at the node, N1. Using
this connection, the currents leaving the
node will be measured. Care must be taken
to never connect the multimeter leads across
a voltage source whenever the multimeter is
not functioning as a voltmeter.
1.
2.
3.
4.
5.
6.
7.
8.
Switch the digital multimeter to the ohmmeter mode.
Measure the three resistors. Enter the measured values into Table 1.
Construct the circuit as shown in Figure 1.
Switch the digital multimeter to the DC ammeter mode.
Measure the four currents. Enter these into Table 1.
Switch the digital multimeter to the DC voltmeter mode.
Measure the circuit voltage from node 1 to node 0. Enter this value into Table 1.
Use the measured voltage and the measured resistance to calculate the theoretical currents.
Enter them into Table 1.
Nominal
Resistance
R1 = 1000Ω
R2 = 2200Ω
R3 = 3300Ω
Table 1. Kirchhoff’s Current Law Data
Measured
Measured
Measured
Resistance
Voltage
Currents
R1 =
IR1 =
R2 =
IR2 =
R3 =
IR3 =
Req =
V=
IV1 =
Theoretical
Currents
V/R1 =
V/R2 =
V/R3 =
ΣV/R’s =
Compare the measured and the theoretical currents. Discuss your findings using Ohm’s law and
Kirchhoff’s current law.
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Kirchhoff’s voltage law will be verified by summing the voltage drops across the four
circuit elements shown in Figure 2. One of these elements is a voltage source and the other three
are resistors. From Kirchhoff’s current law, we can conclude that the current flowing through
each element of the series circuit is the same. This current can be calculated by applying Ohm’s
law; that is, dividing the total applied voltage by the circuit resistance. The voltage across each
resistor can then be found by multiplying the
element resistance by the circuit current.
When these voltages are added, the sum will
equal the total applied voltage. This is
verified in the lab by measuring each
element voltage with a digital voltmeter and
the circuit current with a digital ammeter.
The symbol, V21, designates the
voltage rise between node 1 and node 2.
This is measured by connecting the black
meter terminal to node 1 and the red meter
terminal to node 2. The meter will then read
a positive value if there is a voltage rise or a
negative value if there is a voltage fall.
1. Use the resistors from the previous circuit for this part of experiment. Enter the same set of
measured resistance values into Table 2.
2. Construct the circuit as shown in Figure 2.
3. Switch the digital multimeter to the DC voltmeter mode.
4. Measure the voltage across each of the fours circuit elements being careful to determine the
voltage polarity. Enter these voltages into Table 2.
5. Switch the digital multimeter to the DC ammeter mode. Measure the circuit current and
enter the value into Table 2.
6. Use the measured currents and measured resistance to calculate the theoretical voltages and
enter them into Table 2.
Nominal
Resistance
R1 = 1000Ω
R2 = 2200Ω
R3 = 3300Ω
Table 2. Kirchhoff’s Voltage Law Data
Measured
Measured
Measured
Resistance
Current
Voltages
R1 =
V10 =
R2 =
V21 =
R3 =
V32 =
Req =
I=
V30 =
Theoretical
Voltages
I*R1 =
I*R2 =
I*R3 =
ΣI*R’s =
Compare the measured and the theoretical voltages. Discuss your findings using Ohm’s law
and Kirchhoff’s voltage law.
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