RC Circuits


To determine the time constant of an RC circuit


  • To learn the concept of half-life associated with the exponential function
  • To learn how to plot an exponential function along a log scale so that the graph is a straight line
  • To learn how to use spreadsheet to record, plot, and analyze experimental data


  • Breadboard, a 1,000-Ω resistor, 0.1-μF capacitor
  • Universal 850 Pasco Interface with voltage sensor
  • Two wires to connect the breadboard to the Pasco interface for power


Experimental Setup

Lab Setup Intructions

Use 1,000-Ohm resistor with 0.1 microF capacitor to connect in a RC circuit. Connect the breadboard to the Pasco interface for power and turn the interface on (green light)

In Pasco Capstone:

  • Click on the input where you connected the voltage sensor and select voltage sensor from the drop down menu
  • Click on the upper right corner input (power) and select output voltage current
  • Click on the signal generator icon (bottom of the left menu) and select positive square function with 2000 Hz frequency and 10 V amplitude.
  • Click on the bottom part of the window to change the measuring frequency to 500 kHz
  • Click on the bottom of the screen (recording conditions) and select “end conditions” time 0.001 s

Activity 1. Determine the time constant of an RC circuit

Measure the voltage across the resistor as a function of time. Export data for one segment during the voltage drop into spreadsheet. Plot ln V versus time and determine the slope. What is the time constant of the circuit? How does it compare with the values given by the manufacturer.