Course Name : Embedded System and IOT Lab
Course Code : CSE-234
Lab Report no : 03
Submitted By:
Student’s Name : Mohammad Jihad Islam
ID : 221-15-5796
Department : CSE
Section : 61_C
Submitted to:
Mr. Avizit Nandi
Lecturer,
Department of CSE,
Daffodil International University.
Date of Submission: 21/07/2025
Title
Analysis of Capacitor Charging and Discharging Based on Time Constant in an RC Circuit
Objective
● To analyze the behavior of a capacitor during charging and discharging cycles.
● To investigate the effect of different RC values on the circuit’s time constant (τ).
● To examine the exponential voltage response of capacitors over time.
● To compare multiple RC combinations by monitoring voltage changes.
● To practically verify the theoretical RC charging/discharging model using real
measurements.
Theory
An RC circuit is composed of a resistor and a capacitor. When voltage is applied, the capacitor
charges through the resistor; when disconnected, it discharges back through the same path.
The charging or discharging process follows an exponential curve defined by the time constant
(τ = R × C). This value determines how quickly the capacitor charges up to approximately
63.2% of the supply voltage or discharges to 36.8% of its initial voltage. The larger the
resistance or capacitance, the slower the response. This experiment helps visualize this
behavior using voltage-time measurements and allows us to correlate theoretical predictions
with observed data.
Equipment
● Resistors: 1 KΩ, 10 KΩ, 100 KΩ
● Capacitor: 100 μF
● Breadboard
● DC Power Supply (or 9V Battery)
● Multimeter or Oscilloscope
● Switch
● Jumper wires
Circuit Diagram
Data Table
Time (s) Voltage (V) - Charge Voltage (V) - Discharge
0 0.00 V 9.00 V
10 5.80 V 3.75 V
20 7.20 V 1.90 V
30 8.10 V 0.95 V
40 8.60 V 0.50 V
50 8.85 V 0.25 V
Graph
Discussion
In this experiment, we observed the exponential nature of capacitor charging and discharging.
Initially, the capacitor voltage increased rapidly, then gradually slowed as it approached the
supply voltage. The discharging followed a mirrored path, where the voltage dropped rapidly at
first, then slower over time. Using the formula τ = RC, we noticed that a larger resistance or
capacitance caused the voltage to change more slowly, increasing the time constant. The
recorded voltage values aligned well with theoretical predictions. This validates the RC circuit’s
importance in practical timing and signal-processing applications.
Conclusion
The lab effectively demonstrated the concept of time constant in an RC circuit. By measuring
voltages at defined time intervals and comparing the charge-discharge curves, we confirmed the
exponential behavior predicted by the RC time constant formula. This knowledge is essential in
the design of filters, timers, and analog-to-digital interfacing in embedded systems and IoT
devices. Through this experiment, we gained hands-on experience and a clearer conceptual
understanding of how resistors and capacitors interact over time.
