When light of a single color (or wavelength) passes through the layer of air between two flat pieces of glass, part of the light is reflected by the glass-to-air boundary and part is reflected from the air-to-glass boundary. If the difference in the paths of the two rays is equal to a multiple of whole wavelengths, the light amplitude will add to form a bright band. Students will observe the differences between looking at the light through high-quality glass and low-quality glass.
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This activity is part of the Optics Educator Guide