Thin film interference Classes Used: PHYS 101, PHYS 158

interference

To show the interference fringes produced by a thin soap bubble.

Metal ring and solution, Lens, 35 mm projector, various stands and clamps, coloured filters.

A solution is made out of dish soap, water, and glycerin to help prolong the life of the bubble. The metal ring is dipped into a soap solution and the projector light is directed on to the soap bubble and the reflection is focused on the wall using a lens. With white light, coloured horizontal fringes can be seen. With the yellow filter a series of yellow and black fringes are seen of varying width as the soap bubble drains leaving the thinnest film at the top.

Students must be reminded that the lens has inverted the image. The thinnest portion of the film will therefore be seen at the bottom on the screen as an extended black area just before the bubble breaks.

General Location: There are many parts for this demo and nothing is specifically set aside. There are many pictures below that will hopefully aid in constructing this demonstration. This demonstration could be made with simple house-hold products. The projector is found in the blue closet floor. Clamps and such can be found at the back of the room, while glycerin can be found in the fume hood. Updated on: 01/13/17