5L30.20 - Blinky Whirligig - AC Made Visible

Code Number:
Demo Title:
Blinky Whirligig - AC Made Visible
AC vs. DC
Area of Study:
Electricity and Magnetism
Demo Board with 3 VDC Battery, 3 V Transformer, Wave Generator, and Power Cord with Bi-Color LED.

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.

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Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.