Experiment # 04
Circuit Theorems
Object:



Illustrate the superposition theorem.
Thevenin’s and Norton's theorem.
Reciprocity theorem for linear circuits
Apparatus:






Dual DC power supply (0-20V).
Multimeter.
Ohmmeter.
Three-port resistor network.
Circuit board.
Different resistors.
Experimental set-up and procedure:
I. Two-port resistor network
Consider a two-port resistor network as in Fig. 1.
R3
R1
1
R2
R4
2
Fig.1
1. Set up the circuit in Fig. 1.
2. Connect port 1 to a DC power supply (voltage source).
3. What is Thevenin's, and Norton's theorems?
4. Calculate the Thevenin and Norton equivalents of this circuit.
5. Take the necessary measurements to determine the Thevenin and Norton equivalents of this circuit.
6. Explain why you took such measurements.
7. Give the % errors on the measured values.
I-Three-port resistor network
Consider the 3-port resistor network shown in Fig. 2.
3
1
2
Fig.2
a) Superposition theorem
1. Apply different voltages V2 at port 1 and simultaneously apply V3 at port 3
2. Measure the short circuit current Isc at port 1 and record your values in Table 1
EGR 2402 Laboratory Manual
22
3. Disconnect the power supply from port 2
4. Measure the current I2 at port 1 when port 2 is shorted out for the difference values of V3
5. Disconnect the power supply from port 3
6. Measure the current I3 at port 1 when port 3 is shorted out for the different values of V2
7. Calculate the % error on Isc and record all your values in Table 1:
V2 (Volts)
V3 (Volts)
2
3
4
5
6
15
15
6
20
2
I2
I3
I2+I3
Isc
% Error
8. What is the superposition theorem?
9. Does it hold in this case? Explain
b) Thevenin and Norton theorems
1. Connect a DC power supply to port 1 and apply a voltage V1 = 10V
2. Short-circuit the terminals in port 3
3. At port 2, measure the open circuit voltage V2 and the short-circuit current I2
4. Find the Thevenin and Norton parameters for port 2
5. Disconnect the power supply from port 1
6. Connect to port 1 a resistance equal to the power supply internal resistance
7. Measure the total resistance RT of the circuit at port 2
8. Compare RT to the Thevenin resistance RTh and give the % error
9. Complete Table II:
V1 (Volts)
10
V2
12
RT
RTh
% error
10. Does Thevenin's and Norton's theorems hold? Explain
c) The reciprocity theorem
1. Place the DC power supply at port 1 and apply different voltages U.
2. Short circuit the terminals at port 3
3. Connect an ammeter to port 2 and measure the current I2
4. Interchange the voltage source and the ammeter and measure Il
5. Compare I2 to I1 and give the % difference
6. Record your measurements in Table III :
U (Volts)
I1
I2
% Difference
2
5
10
15
20
7. What is the reciprocity theorem?
8. Is this theorem obeyed here? Explain?
9. What could be the main origin of the calculated % difference?
Conclusion:
1. What did you learn from these experiments? Explain and give some applications?
3. What could we place inside the three-port networks to make it not satisfy some of these circuit
theorems? Explain ?
EGR 2402 Laboratory Manual
23
Experiment # 04
Name:
Section:
Circuit Theorems
I. Two-port resistor network
5. Thevenin and Norton parameters
II. Three-port resistor network
a) Superposition theorems
V2(volts)
V3 (Volts)
2
3
4
5
6
15
15
6
20
2
I2
I3
I2+I3
% Error
RT
Rth
% Error
b) Thevnin and Norton theorems
V1(Volts)
V2
I2
c) The reciprocity theorem:
U (Volts)
I1
I2
% Difference
2
5
10
15
20
EGR 2402 Laboratory Manual
24