EC1022 – Electrical
Systems
Lab 6
RC and RL Circuits
Name: Perera W.S.O
ID number: EN23467866
Date of Submission: 26/10/2023
Objective
The objective of this lab exercise is to identify how to construct RC and RL circuits and analyze
their waveforms through the oscilloscope. Furthermore, this lab is held to provide an
understanding between voltage and current behaviour in RC and RL circuits while also showing
the relationship between frequency and the output voltage between reactive components.
Introduction
In this lab report, we examine how two significant circuits—the RL (Resistor-Inductor) and RC
(Resistor-Capacitor) circuits—behave under various frequency conditions produced by a function
generator.
An electrical component that stores electrical energy in an electric field is called a capacitor.
Capacitors are primarily used to store and release electrical charge and energy. The electronic
component known as an inductor is used to store electrical energy as a magnetic field. Their main
job is to resist current fluctuations by creating a voltage in reaction to changes in the current that
passes through them.
These circuits differ from normal circuits as capacitors and inductors have reactances while other
circuits have resistances. Furthermore, RC and RL circuits respond differently to varying
frequencies of AC signals. This is because the impedance (the total opposition to current flow) in
these circuits changes with frequency. Other circuits, like purely resistive ones, do not exhibit this
frequency-dependent behavior.
The reactance of an inductor is directly proportional to its frequency, while the reactance of a
capacitor is inversely proportional to its frequency. Therefore, when the frequency is increased,
the output voltage of a capacitor decreases, and the output voltage of an inductor increases.
Moreover, there is a phase difference between voltage and current in RC and RL circuits.
According to theory, voltage leads current by 90° in an inductive circuit, and current leads voltage
by 90° in a capacitive circuit.
Our goal in this project is to build RC and RL circuits and see how they react to various
frequencies. We can precisely adjust the input signal's frequency with a function generator, which
enables us to watch how the voltage across these circuits changes as the frequency is increased.
This study will offer important new understandings of the graphical behavior of RC and RL circuits
when they interact at different frequencies.
Understanding the frequency-dependent behavior of RC and RL circuits is crucial for engineers
and scientists, as it forms the basis for designing and analyzing electronic systems. The results
obtained in this experiment will not only contribute to a deeper comprehension of these circuits
but also enable us to make informed decisions when applying them in practical applications.
This lab report describes the experimental setup, the circuit construction, results, analysis, and
conclusions about the voltage behavior of RC and RL circuits to varying frequencies. Our
knowledge of circuit behavior will be improved by this investigation, which will also lay down the
foundation for upcoming projects in electrical and electronic engineering.
Apparatus
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Function Generator – (SFG-2000/SFG-2100 Series)
Oscilloscope – (Agilent 1000B Series)
2 1KΩ Resistors
100nF Capacitor
1mH Inductor
Jumper Wires
Procedure
1. Construct the two circuits as shown below using the function generator, oscilloscope,
resistors, capacitor, inductor, and jumper wires.
2. Next, switch on the function generator. It should be connected in series to the circuit.
3. Then, switch on the oscilloscope. It should be connected across the 2 terminals of the
inductor and capacitor in their respective circuits.
4. Set the frequency of the circuit to 100Hz using the function generator.
5. Set the peak-to-peak voltage in channel 1 to 10V using the function generator.
6. Observe the input and output waveforms in the oscilloscope.
7. Note down the peak-to-peak voltage of channel 2.
8. Change the settings of the oscilloscope and move the cursors to obtain the phase difference
between the input and output waves.
9. Repeat the procedure for 10,000Hz and 100,000Hz for both RC and RL circuits.
10. Tabulate the values obtained.
Pre – Laboratory Exercise
Calculations
Laboratory Work
Laboratory Exercise I
Observations
10 KHz – RC Circuit
Phase Difference
The phase difference in seconds: 24µs
The phase difference in degrees: 75°-90°

The output waveform is lagging when compared to the input waveform.
Table 1 - The effect of frequency on voltage across the capacitor
Frequency
(Hz)
100
𝑽𝒐𝒖𝒕,𝑪(𝒑) (V)
10,000
𝑉𝑝 − 250m
𝑉𝑝−𝑝 - 500m
100,000
𝑉𝑝 − 150 m
𝑉𝑝−𝑝 - 300m


Waveform
𝑉𝑝 − 4.3
𝑉𝑝−𝑝 - 8.6
When we constructed the circuit, there was a lag between the input and output voltages.
The output waveform was lagging when compared to the input waveform. This is because
current leads voltage by 90°.
When we increased the frequency, the output voltage across the capacitor decreased. This
is because the reactance of the capacitor is inversely proportional to its frequency. As
capacitor voltage is proportional to reactance, its voltage is inversely proportional to the
frequency.
Laboratory Exercise 2
10 KHz – RL Circuit
Phase Difference
The phase difference in seconds – 24µs
The phase difference in degrees - 70°- 90°
Table 2 - The effect of frequency on voltage across the inductor
Frequency
(Hz)
100
𝑽𝒐𝒖𝒕,𝑳(𝒑) (V)
Waveform
𝑉𝑝 − 68m
𝑉𝑝−𝑝 - 136m
10,000
𝑉𝑝 − 376m
𝑉𝑝−𝑝 - 752m
100,000
𝑉𝑝 − 2.64
𝑉𝑝−𝑝 - 5.28

When we constructed the circuit, there was a lag between the input and output voltages.
The output waveform was leading when compared to the input waveform. This is because
voltage leads current by 90°.

When we increased the frequency, the output voltage across the inductor increased. This is
because the reactance of the inductor is directly proportional to its frequency. As inductor
voltage is proportional to reactance, its voltage is directly proportional to the frequency.
Post Laboratory Exercise
Results
1. Compare the theoretical and practical values obtained and comment on that.
Table 3 - Comparison between theoretical and practical values
Type
Theoretical
Practical
Capacitor
1.57 V
Phase difference: 90°(input leads)
0.50V
Phase difference: 75° - 90°(input leads)
Inductor
0.627
Phase difference: 90°(output leads)
0.752 V
Phase difference: 70°- 90°(output leads)
In both circuits, there are deviations between the theoretical and practical values. In the inductor,
the practical value is larger than the theoretical value. In the capacitor, the practical value is smaller
than the theoretical value. The values are different because there may have been internal
resistances in the constructed circuit, loose connections, and failures in the probes of the
oscilloscope. Also, electrical noise can affect the measurement.
The theoretical and practical phase difference values were similar under the range of experimental
accuracy.
2. Comment on the effect of frequency on the output voltage of each circuit.
Capacitor
When we increased the frequency, the output voltage across the capacitor decreased. This is
because the reactance of the capacitor is inversely proportional to its frequency. As capacitor
voltage is proportional to reactance, its voltage is inversely proportional to the frequency.
Inductor
When we increased the frequency, the output voltage across the inductor increased. This is because
the reactance of the inductor is directly proportional to its frequency. As inductor voltage is
proportional to reactance, its voltage is directly proportional to the frequency.
Discussion
In both circuits, there are deviations between the theoretical and practical values. In the inductor,
the practical value is larger than the theoretical value. In the capacitor, the practical value is smaller
than the theoretical value. The values are different because there may have been internal
resistances in the constructed circuit, loose connections, and failures in the probes of the
oscilloscope. Also, electrical noise can affect the measurement.
We had to assemble the circuit and connect the voltage supply across the inductor and capacitor
respectively. Then we had to change the frequency while keeping the input voltage constant and
we had to observe the waveform from the oscilloscope from the readings.
I learned that the input signal lags with respect to the output signal in the inductor and the input
signal leads with respect to the output signal in the capacitor. This is because current leads voltage
by 90° in a capacitor and voltage leads current by 90° in an inductor. We learned how to construct
RC and RL circuits and connect the oscilloscope across them to calculate the output voltage. I
understood that there is a phase difference between the input and output signals of an inductor and
capacitor, and I further expanded my knowledge regarding how to operate the oscilloscope to get
the phase difference and input and output voltages. There was a sound from the oscilloscope when
we were taking readings. This was because of some loose connections in the circuit. Furthermore,
I learned about the effect of frequency on the voltage across inductors and capacitors. In addition,
I also gained experience in drawing phasor diagrams through this lab exercise.
Conclusion
We learned how to assemble RC and RL circuits, take voltage readings for them through the
oscilloscope, and identify the relationship between frequency and output voltage in the respective
circuits.
The key outcomes of this exercise were:
RC Circuit: 1. The input signal leads the output signal.
2. When frequency increases, the voltage across the capacitor decreases
RL Circuit:
1. The output signal leads the input signal.
2. When frequency increases, the voltage across the inductor increases