Procedure: 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 bubble-making solution with the
wire loop included for a very small cost.)
Question 1: 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.
Question 2: 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.
Question 3: Try illuminating your soap film first with a frosted
incandescent lamp and then with a fluorescent lamp. Describe the
differences that you see.