Final answer:
Two samples in an experiment are commonly spotted onto a sheet of paper, thin aluminum plate, or between microscope slides to observe thin film interference, which reveals interference patterns that can measure tiny distances.
Step-by-step explanation:
When conducting experiments involving thin film interference, two samples are often spotted onto a thin material such as a sheet of paper, a thin aluminum plate, or using microscope slides. In the context of a physics experiment such as the one described in figure 27.34, thin film interference is observed when two very flat glass microscope slides are separated, creating a wedge of air between them. As the thickness of this air wedge changes uniformly, interference patterns are produced due to phase changes occurring at different surfaces. These patterns may appear as dark and bright bands or even rainbow colors, especially when white light is used. These bands can reveal information about minute distance changes and can even help measure objects like debris that cause the separation between the slides.