Demos: 7A-06 Multiple Images
Simulating a kaleidoscope, a candle is placed is placed between two hinged, plane mirrors. Depending on the angle between the mirrors, a number of multiple images is seen. A laser beam aimed at any of the images will illuminate the candle itself, illustrating the law of reflection.
Directions: Dim the room lights. Set the mirrors at about a 60° angle. Move to the front of the lecture desk and sit below the level of the desk so as not to obstruct the view. Shine the laser beam onto the candle, causing it to glow. Then aim the beam at any one of the images. The candle still glows. The lec-demo tech will create a dust cloud so that the laser beams reflection can be seen clearly. Changing the angle between mirrors will change the number of images seen.
Suggestions for Presentation: Ask if the students have seen a kaleidoscope. Show them how the candle images can be created by having multiple reflections in the two mirrors. Using a laser instead of lighting the candle does two things: it causes the entire candle wax to glow and it allows you to trace the reflected beams in the dust (which the students really enjoy!).
This is a good time to introduce the principle of reversibility of a light path. The light coming to your eye from the direction of the image is the final reflected ray. If you direct the laser beam along that path it will end at the candle. The dust allows you to show this. Simply aim the laser beam at the image and the candle will glow. A nice effect.
Applications: Kaleidoscopes and multiple mirrors, such as those in clothing stores.