It is a simple matter to produce soap films that demonstrate thin-film interference phenomena. Place a few drops of liquid dish-washing detergent in a shallow bowl and add enough water to form a reasonably fluid solution. Bend a piece of wire into a closed loop, leaving a small length to serve as a handle. (Alternatively, you can purchase bubblemaking solution with the wire loop included for a very small cost.)
a. Dip the loop in the soap solution to form a soap film in the plane of the loop. Reflect light from a desk lamp from the film. Describe the colored patterns that you see.
b. If you hold the loop in a vertical plane, the colors should settle into a pattern of horizontal bands. Sketch the bands that you see indicating both their color and width. Explain why we get horizontal bands.
c. Try illuminating your soap film first with a frosted incandescent lamp and then with a fluorescent lamp. Describe the differences that you see.