RC Circuits

Review material related to RC circuits before beginning this simulation. You will need to download
the files RC.circuitjs, RCparallel.circuitjs, and RCseries.circuitjs from canvas in order to do this
simulation.
Part 1: RC Circuit
1. Navigate to https://www.falstad.com/circuit/
2. Click “File”, “Open File”, and open the “RC.circuits,js” file
3. When one full cycle of the signal from the bottom oscilloscope is visible, click “RUN/STOP”.
4. Record the value of the resistor and the capacitor.
5. The half time of an RC Circuit can be measured by observing the time it takes for a capacitor to
charge or discharge half of its maximum voltage. When the capacitor is charging, the voltage
over the capacitor begins to increase from its minimum value to its maximum value. When the
capacitor is discharging, the voltage starts at its maximum value and decreases to its minimum
value.
6. In this simulation, the capacitor reaches half of its maximum value when it crosses the x axis of
the oscilloscope plot. Using your cursor, mouse over the signal when the capacitor is at its
minimum value. Do the same to find the time when it reaches half of its maximum value while it
is charging, the time at its maximum value, and the time will it is at half its maximum value while
discharging. Record these in the table below and calculate the half time of the circuit (1/2 Time)
when the capacitor is charging and discharging.
R
C
Time at Vmin
Time at ½ Vmax (charging)
Time at Vmax
Time at ½ Vmax (discharging)
½ Time (charging) = time at ½ Vmax (charging)
– time at Vmin
½ Time (discharging) = time at ½ Vmax
(discharging) – time at Vmax
Name:_________________________ Section:________________
7. The theoretical time constant of the circuit is given by the equation:
=
Where R is the value of the resistor and C is the value of the capacitor. It can also be calculated
experimentally from the half time of the circuit:
=
1/2
0.69
Compute the theoretical value of τ, along with the experimental values of τ from your charging
and discharging half times. Average the value of your charging and discharging time constants
and calculate a percent difference to the theoretical value of the time constant. Fill these in the
table below. Show your work below.
τcharge
τdischarge
τavg
τtheoretical
% Difference
Part 2: Parallel RC Circuit
1. Open the file “RCparallel.circuitjs”
2. In this instance, there is a resistor in parallel with the two capacitors that are in parallel. This
resistor has a very high resistance. Because it is in parallel with the two capacitors, it acts like a
voltmeter, measuring the potential across the two capacitors. Measure the half times for the
charging and discharging cycles of the two capacitors in parallel and fill in the rest of the table.
Because the two capacitors are in parallel, you will need to calculate the total capacitance of the
circuit with the equation:
= 1 + 2
R
C1
C2