6D30.20 - Thin Film Interference - Soap Films

Code Number:
Demo Title:
Thin Film Interference - Soap Films
Thin Film Interference
Area of Study:
Enclosed Box with Bubble Maker and Bubble Liquid, Film Strip Projector, 8 Inch by 8 Inch 252 mm lens, Bubble Blowing Liquid, Bubble Blowing Rings and Accessories, Fluorescent Light (If Needed), Video Camera and Power Supply, Book: Soap Bubbles by C. V. Boys, Focusing Lens, and Bubble Kit, 2-L Bottle with Hole in Bottom.

The enclosed box with bubble maker and bubble liquid should be ready to go with no preparation.  The procedure is to shoot light from the projector into one face of the box, and the image of the bubble will be reflected onto a screen at a 90 degree angle to the incident light.  This is due to the bubble maker being set at a 45 degree angle inside the box.  The large 8 inch by 8 inch, 252 mm lens is then used to focus the reflected image on the screen.

For the classroom conditions that we usually experience a bubble mixture of our own making seems to work best.  The mixture is as follows: 8 oz. of 'Wonder Bubble', 1 to 2 oz. of 'Joy' dishwashing Liquid, 1 to 2 oz. of Glycerin.  To observe better thin film interference use 2 to 3 times as much glycerin.  When you want to observe thin films influenced by gravity, support the bubble ring on a stand and look through the film onto a white screen background.  The pattern can be easily seen in reflected light.  A bubble will also show the interference pattern, but is usually harder to view or project.

An inexpensive bubble holder that will enclose the bubble and make it last for long periods of time can be made from a 2-L bottle.  Poke a hole in the bottom of the bottle and suck the soap film in through the mouth.  When the bubble is well into the bottle, screw on the cap.  This can be used on the overhead projector.

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Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.