Electric Circuits Lab

Series RL Circuits: Phase Angle, Phase Lead, and Inductors as Differentiators

I. Objectives:

After completing this lab experiment, you should be able to:

1. Understand the effect of frequency on inductive reactance.

2. Measure the impedance of an RL circuit.

3. Measure the phase angle and phase lead of an RL circuit using the oscilloscope.

4. Draw the impedance and voltage phasor diagrams.

5. Understand how an inductor differentiates current.

II. Parts List:

1. Resistors 100 Ω, 1 kΩ, 10 kΩ.

2. Inductors 1 µH, 100mH.

III. Procedures:

Part I :

1. Connect the following circuit.

Figure 1: RL Circuit

2. Connect one DMM across the resistor and one DMM across the inductor. 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 RL circuit, the same current will flow through the inductor and the resistor. Record the result in Table 1.

Total current I =

4. Calculate the inductive reactance using Ohm’s law. Record the result in Table 1.

Inductive Reactance XL =

5. Finally, calculate the inductive reactance using the inductive reactance equation. Record the result in Table 1.

Inductor L1

Voltage across, R

845.958 mV

Voltage across, L

533.246 mV

Total Current, I

0.846 mA

Inductive Reactance, XL

630.35 ohms

Computed Reactance, XL

628.32 omhs

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 inductor. Record your measurements.

Frequency (in Hz)





I =

XL =

XL = 2πfL



982.58 mV

185.81 mV

0.9856 mA

189.10 ohms

188.50 ohms


845.958 mV

533.246 mV

0.846 mA

630.35 ohms

628.32 ohms


467.467 mV

833.996 mV

0.468 mA

1.78 kΩ



302.425 mV

953.161 mV

0.302 mA

3.15 kΩ

3.14 kΩ


221.027 mV

975.265 mV

0.221 mA

4.41 kΩ

4.40 kΩ


173.593 mV

984.811 mV

0.174 mA

5.66 kΩ

5.66 kΩ


142.743 mV

989.751 mV

0.143 mA

6.92 kΩ

6.91 kΩ


121.133 mV

992.626 mV

0.121 mA

8.20 kΩ

8.17 kΩ


105.174 mV

994.442 mV

0.105 mA

9.47 kΩ

9.43 kΩ

Table 2: Calculated and measured values

7. Plot the graph for Frequency vs. VL.

(Use Word or Excel to create the plot)

Figure 2. Plot of Frequency vs. Inductor Voltage

Part II:

8. Build the circuit in Figure 2.

Diagram, schematic  Description automatically generated

Figure 2: Series LR Circuit

9. Set the voltage source amplitude to 1.5 VP and frequency to 25 kHz, sine wave