5F30.60 - Relaxation Oscillators - Neon Bulb, Doorbell, and Strobe Lights

Code Number:
Demo Title:
Relaxation Oscillators - Neon Bulb, Doorbell, and Strobe Lights
Relaxation Oscillators
Area of Study:
Electricity and Magnetism
Neon Bulb Relaxation Oscillator Circuit, Variable Strobe Light Kits.

Video Credit: Jonathan M. Sullivan-Wood.

Connect the DC voltage source and turn up to the voltage indicated.  The neon bulb should flash with a rate of 2 to 5 seconds.  Changing the size of the resistor will change the time of oscillation.

The variable rate strobe units are the same as the neon circuit in that a capacitor charges and at some threshold voltage the strobe bulb triggers.  The capacitor voltage then falls and starts to recharge to the threshold voltage again.  The potentiometer control varies the resistor value and thus changes the charging time.  

A simple homopolar motor is made by attaching a magnet to the negative end of a AA battery and dropping the spiral copper spring over the battery.  Place a small dimple in the positive pole of the magnet to keep the spring centered while it rotates.  Observe the rotating coil closely and you will see it jump up and break contact repeatedly due to the slight contractions of the spring like coil when it is energized.

  • Stanisław Bednarek, "Amazing Vibrations Within the Homopolar Motor", TPT, Jan. 2018, Vol. 54, #1, Jan. 2018, p. 47.
  • George M. Caplan, "Simple DC Power Supply", TPT, Vol. 46, #1, Jan. 2008, p. 57.
  • Paul Chagnon, "Animated Displays V: Relaxation Oscillators", TPT, Vol. 32, # 7, p. 432- 436, Oct. 1994.
  • Richard Crane, "What Does the Drinking Bird Know About Jet Lag?", TPT, Vol. 27, #6, Sept. 1989, p. 470.
  • Earl M. Sawyer, "The Perpetual Light", TPT, Vol. 10, #7, Oct. 1972, p. 362.
  • Zenon Gubanski, "Capacitance by Relaxation Oscillations", TPT, Vol. 9, #2, Feb. 1971, p. 105 & TPT, Vol. 41, #2, Feb. 2003, p. 123.
  • Paul J. Ring, "Lecture Demonstration of the Validity of the Rules for Finding Equivalent Resistance and Capacitance", AJP, Vol. 46, #7, July 1978, p. 762.
  • D. Rae Carpenter Jr. and Richard B. Minnix, "E-240. Relaxation Oscillator", DICK and RAE Physics Demo Notebook, 1993.
  • D. Rae Carpenter Jr. and Richard B. Minnix, "E-400. Relaxation Oscillator w/Scope", DICK and RAE Physics Demo Notebook, 1993.
  • E-4f: "A Flashing Neon Light", Wallace A. Hilton, Physics Demonstration Experiments, p. 73.
  • Robert L. Wild, "150: RC Circuit-Relaxation Oscillator", Low-Cost Physics Demonstrations, p. 88.
  • "The Neon-Tube Relaxation Oscillator", The Physics Instructional Resource Association (PIRA) Newsletter, Vol. 3, #3, May 1988, p. 2.
  • Forrest M. Mims, "The Neon Glow Lamp", Experimenter's Corner, Dec. 1976, p. 111.

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