Experiment # 1
Ohm’s Law & Kirchhoff’s Laws
Objective:
The objective is to study and verify Ohm’s law, Kirchhoff’s voltage law (KVL) and
Kirchhoff’s current law. This will be accomplished by first analyzing the circuits “by
hand”, and then using PSpice. This procedure is known as the preliminary lab exercise
or “Pre-Lab”. As it’s name indicates, it is normally to be completed prior to coming to
lab. (This week, those of you with the Tuesday lab may not have the knowledge base to
complete all of the pre-lab calculations prior to lab. Do what you can and get that part
initialed in lab, then complete the remaining portion of the pre-lab after Wednesday’s
lecture) The “real-world” versions of these same circuits will then be built and examined
in the lab. The theoretical, simulated, and experimental values will then be compared and
discussed in your lab write up.
Preliminary Lab Exercise:
Ohm’s Law:
The three circuits that will be used to verify Ohm’s law are shown in the following
figure:
VS1
15 V
R1
A
I1
VS1
R1
I2
Is
4.7 k
15 V
15 V
5.6 k
B
Circuit (i)
I3
VS1
R2
4.7 k
A
Circuit (ii)
I4
R1
R2
4.7 k
5.6 k
B
Circuit (iii)
(Note: If the arrows do not show up on these figures, positive currents flow from left to
right and from top to bottom)
1. For circuit (i), compute the value of I1.
2. For circuit (ii) compute the value of the current I2. Note that resistors in series add
linearly (that is, the combined resistance measured from terminals A and B is
given by RAB = R1 + R2). Also compute the voltage across the resistor R2.
3. For circuit (iii) compute the value of the currents Is, I3, and I4. Note that resistors
in parallel add in an inverse fashion [that is, the resistance measured across
terminals A and B is given by 1/RAB = 1/R1 + 1/R2, equivalently, RAB=
(R1R2)/(R1+R2)].
4. Use PSPICE to construct the above circuits and run the dc analysis. Compare the
results with the results obtained in steps 1, 2, and 3. Take help of your Lab
Instructor to run the PSPICE simulation.
Kirchhoff’s Laws:
The circuit that will be used to verify Kirchhoff’s Voltage Law (KVL) and
Kirchhoff’s Current Law (KCL) is shown in the following figure:
I1
R1
I3
2.2 k
VS1
15 V
R3
I5
20 k
I2
R5
4.7 k
I4
R2
R4
36 k
10 k
1. Compute the value of currents I1, I2, I3, I4, and I5 by using KVL and KCL. To
solve for the five unknown currents, you may use any method you know of
solving five simultaneous equations. MATLAB can be one of the options.
2. Compute the value of the voltages VR1, VR2, VR3, VR4, and VR5 by using Ohm’s
Law and the values from step 1.
3. Use PSPICE to construct the above circuit and run the dc analysis. Compare the
results with the results you have obtained in steps 1 and 2.
Procedure:
Verification of Ohm’s Law:
1. Construct circuit (i) shown in the figure by connecting the voltage supply across
the resistor R1. Set the voltage supply to 15 V. Use the digital multi-meter to
measure the current I1 by placing it in series with the resistor R1.
2. Construct circuit (ii) shown in the figure by connecting the two resistors R1 and
R2 in series. Connect the voltage supply across the two resistors. Set the voltage
supply to 15 V. Use the digital multi-meter in ammeter mode to measure the
current I2 by placing it in series with the resistor R1. Use the same digital multimeter in voltmeter mode to measure the voltage across the resistors R1 and R2.
3. Construct circuit (iii) shown in figure by connecting the two resistors R1 and R2
in parallel. Connect the voltage supply across the two resistors. Set the voltage
2
supply to 15 V. Use the digital multi-meter to measure the currents Is, I3 and I4
by placing it in series in the appropriate branch of the circuit.
Verification of Kirchhoff’s Laws:
1. Construct the circuit shown in the figure for Kirchoff’s Law. Set the voltage
supply to 15 V. Use the digital multi-meter in ammeter mode to measure the
currents I1, I2, I3, I4, and I5 by placing it in series with the respective component.
2. Use the digital multi-meter in voltmeter mode to measure the voltages VR1, VR2,
VR3, VR4, and VR5 by placing the voltmeter in parallel with the respective
component.
Analysis:
Ohm’s Law:
1. For circuit (i), compare the measured value of I1 to the theoretical value.
2. For circuit (ii), compare the measured values of I2, VR1 and VR2 to the
theoretical values.
3. For circuit (iii), compare the measured values of Is, I3 and I4 to the theoretical
values.
4. Has Ohm’s law been verified? Why?
Kirchhoff’s Law:
1. Verify KVL by summing the voltages around the three loops. Identify three
additional loops and verify that KVL is also satisfied for those loops.
2. Verify KCL by summing the currents flowing in and out of every node.
3. Have Kirchoff’s laws been verified.
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