Electric Circuits Lab
Series RC Circuits: Phase Angle, Phase Lag, and Capacitors as Integrators
I. Objectives:
After completing this lab experiment using, you should be able to:
1. Understand the effect of frequency on capacitive reactance.
2. Measure the impedance of an RC circuit.
3. Measure the phase angle and phase lag of an RC circuit using the oscilloscope.
4. Draw the impedance and voltage phasor diagrams.
5. Understand how a capacitor integrates current.
II. Parts List:
1. Resistor 100 Ω, 1 kΩ, 6.8 kΩ
2. Capacitors 0.1 µF, 0.01 µF
III. Procedures:
Part I:
1. Connect the following circuit.
Figure 1: RC Circuit
2. Connect one DMM across the resistor and one DMM across the capacitor. Set both DMMs to read AC voltage. Measure the voltage drop across each component. Record the result in Table 1.
3. Use Ohm’s law to calculate the current flowing through the resistor. Since the circuit in Figure 1 is a series RC circuit, the same current will flow through the capacitor and the resistor. Record the result in Table 1.
Total current, I =
4. Calculate the capacitive reactance using Ohm’s law. Record the result in Table 2.
Capacitive Reactance, XC =
5. Now, calculate the capacitive reactance value using the equation below. Record the result in Table 1 under Computed Reactance, XC.
Capacitive Reactance,
Capacitor C1
Voltage across, R
846 mV
Voltage across, C
583 mV
Total Current, I
0.846 mA
Capacitive Reactance, XC
686 Ω
Computed Reactance, XC
Table 1: Calculated and measured values
6. Adjust the function generator frequency following the steps in Table 2. Use the DMM to measure the voltage across the resistor and the capacitor. Record your measurements below.
Frequency (in Hz)
VR
(measured)
VC
(measured)
XC =
(calculated)
300
983 mV
186 mV
0.983 mA
189 Ω
1k
846 mV
583 mV
0.846 mA
686 Ω
3k
884 mV
468 mV
0.884 mA
529 Ω
5k
953 mV
302 mV
0.953 mA
317 Ω
7k
975 mV
221 mV
0.975 mA
227 Ω
9k
985 mV
174 mV
0.985 mA
177 Ω
11k
990 mV
145 mV
0.990 mA
147Ω
13k
993 mV
121 mV
0.993 mA
122 Ω
15k
994 mV
105 mV
0.994 mA
106 Ω
Table 2: Calculated and measured values
7. Plot the graph for Frequency vs. VC.
(Use Excel or Word to Create the Plot)
Plot 1: Frequency vs. VC
Part II:
8. Build the circuit shown in Figure 2.
Figure 2: Series RC Circuit
9. Set the source voltage amplitude to 1.5 Vp and frequency to 500 Hz.
10.
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