5L30.20 • Filters and Rectifiers: Blinky Whirlygig

Location: Cabinet 3

Photo of University of Texas at Austin's Demonstration

Instructions / Notes:

• A dual light emiting diode is connected to either a DC or an AC power source.
• The DC power source needs to be connected twice so that the class can see the effect of reversing the current.
• The dual LED changes color when the current is reversed.
• The dual LED is on a long lamp cord so it can be whirled when connected to an AC power source.
• When connected to an AC power source both LED's light up, but not simultaneously.
• By whirling the LED cord with the room lights dimmed, students see a red to green strobe effect.

Video shows student whirling the LED cord at University of Texas at Austin.

Last updated on June 8, 2026