Rotating Two-Color Led
To demonstrate that what comes out of a 110 VAC plug is in fact alternating current.
Red/green bi-color LED wired to 6-volt line transformer.
The bi-color LED is wired across the 110 VAC line. When current flows one direction the red side glows,◙and when current flows the other direction the green side glows, so if it is viewed from a distance the color appears yellow. When the device is swung in a circle the alternating colors become easily visible, indicating that the current in the line is alternating direction.