Blinky Whirligig Setup
Power Cord with Bi-Color LED
Function Generator & LED

 

Code Number: 5L30.20

Demo Title: Blinky Whirligig - AC Made Visible

Condition: Excellent

Principle: AC vs. DC

Area of Study: Electricity and Magnetism

Equipment: 

Demo Board with 3 VDC Battery, 3 V Transformer, Wave Generator, and Power Cord with Bi-Color LED.

Procedure:

Plug the bi-color LED into the DC battery and show that orientation makes a difference to whether you see green or red.  When you plug the LED into the transformer you see what appears to be green and red simultaneously.  However, if you move the light back and forth or twirl it in a circle, you will see alternating strips of red and green with a dark band in between.  This dark band is the interval when the sine wave voltage is not enough to light the LED.

An interesting variation is to replace the transformer in the above mentioned demonstration with a wave generator.  With a 60 Hz. sine wave you will see the dark spaces between the red and green bands of light when you twirl the LED.  Keep twirling the LED and switch the wave generator from sine wave to square wave and observe that the dark spaces disappear.

References:

  • John Carlson, "Alternating-Current Demonstration Using Christmas Tree Lights", TPT, Vol. 50, #5, May 2012, p. 315.
  • Paul Hewitt, "Figuring Physics: Flash Frequency", TPT, Vol. 50, #4, Apr. 2012, p. 202.
  • Steve Colletti and Jay Walgren, "A New Spin on an Old Demo", TPT, Vol. 48, #6, Sept. 2010, p. 427.
  • Marcelo M. F. Saba and Daniel D. Monteiro, "Color Addition and Alternating Current", TPT, Vol. 38, #7, Oct. 2000, p. 446.
  • John W. Jewett Jr., "Get the LED Out", TPT, Vol. 29, #8, Nov. 1991, p. 530.
  • Walter Connolly and Ray Watterson, "Tri-Color LED Demonstrator", TPT, Vol. 25, #4, Apr. 1987, p. 234.
  • Gerard Lietz, Anthony Behof, and Marshall Ellenstein, "Illuminating Standing Waves", TPT, Vol. 24, #7, Oct. 1986, p. 449.
  • Walter Connolly, "Tri-Color Demonstrator", TPT, Vol. 23, #9, Dec. 1985, p. 558.
  • Jay S. Huebner, "More on AC", TPT, Vol. 22, #9, Dec. 1984, p. 554.
  • Lloyd Harrich, "AC Made Visible", TPT, Vol. 22, #7, Oct. 1984, p. 448.
  • Karl C. Mamola, "Plastic Discharge Tubes", TPT, Vol. 16, #4, Apr. 1978, p. 241.
  • Robert F. Neff, "Tricks of the Trade: Simple  AC Demonstrator", TPT, Vol. 12, #9, Dec. 1974, p. 574.
  • T. L. Rokoske and R. C. Nicklin, "Glow Lamp Swingers", AJP, Vol. 43, #1, Jan. 1975, p. 112.
  • "B-410. Diodes and Gas-Filled Tubes", DICK and RAE Physics Demo Notebook, 1993.
  • Jodi and Roy McCullough, "A.C. Circuits with a Flicker Bulb", The Role of Toys in Teaching Physics, p. 4.186.
  • Borislaw Bilash II and David Maiullo, "AC Blinkies", A Demo a Day: A Year of Physics Demonstrations, p. 284.
  • "Concepts in Motion: The Blinky", The Project Physics Course - Teachers Resource Book, p. 109.
  • Robert Ehrlich, "L.12. Twirling a Neon Lamp on a Line Cord", Turning the World Inside Out and 174 Other Simple Physics Demonstrations, p. 153 - 154.