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When a laser light is reflected from a vibrating membrane, it produces beautiful patterns on the screen. Here, a flat membrane is formed by fitting a balloon's elastic rubber on a PVC pipe. The elastic membrane is vibrated by producing sound waves on the other end of the pipe. A mirror fitted on the membrane reflects the laser light. A wall acts as the screen.
Take a tin can or plastic pipe of 3-4 inch long. Remove both ends to make it a hollow cylinder. Take a balloon and stretch it over the can, then wrap a rubber band around the balloon. Take a small piece of mirror. Use a drop of glue to stick the piece of mirror to the balloon. Allow the light through a slit (or laser light) to fall on the mirror. After reflection the light spot is seen on the wall. Talk or shout directly into the open end of the can and observe the dancing light spot on the wall. Discuss with your friends what makes the light spot dance.
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