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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