5F30.20-Charge and discharge an RC circuit


Video: Watch this demo

Description: Use the oscilloscope to show V(t) for a capacitor charging and discharging in an RC circuit.


  • capacitor (in video: 1 μF, Vmax = 63 V) in wood block
  • resistor (in video: 100 Ω) in wood block
  • square wave function generator
  • oscilloscope
  • (x1) BNC to banana plug adapter (for scope)
  • (x3) banana plug cords

Setup Procedure:

  1. Place function generator on table where it can be easily accessed by the professor.
  2. Place scope where it can be easily seen by the class (or by a video camera).
      1. ***SAFETY CHECK***
    1. Connect oscilloscope directly to function generator
    2. Set function generator to 0 dB attenuation, and minimum amplitude.
    3. Slowly increase function generator amplitude and use scope to measure the voltage.
    4. When a safe, but appropriate amplitude is reached, LEAVE THE AMPLITUDE AND ATTENUATION AT THESE SETTINGS.
    5. Disconnect scope from function generator.
  3. Connect function generator output to resistor and capacitor, all in series.
  4. Connect scope input across capacitor in parallel.
  5. Set function generator to square wave, f1/(20RC) (in photo, video: f = 530 Hz)
  6. Set oscilloscope to appropriate Volts per division, sweep ≈ 40RC (in photo: sweep = 0.5 ms).
  7. Plug in equipment and turn on function generator and scope.

Demonstration Procedure:

  1. Turn on all the equipment, and observe the charge/discharge curve. It should be set to the proper settings already.
  2. If you want, you can adjust the oscilloscope settings and/or the function generator FREQUENCY (please don’t change the amplitude, because it may damage the capacitor and could cause injury!)