lecture27_part_2_.ppt
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Light undergoes a phase change of 180° or π radians when reflecting from a medium with a higher refractive index. When reflecting from a medium with a lower refractive index, there is no phase change. This phase change causes reflected waves to be either in phase or out of phase, resulting in constructive or destructive interference in thin film interference situations.
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lecture27_part_2_.ppt
- 1. y = A sin (kx - t)
- 2. Light undergoes a phase change of 180° ( radians) upon reflection from a medium that has a higher index of refraction than the one in which the wave is traveling. Applet. Interference from Reflection Thin Film Interference: Phase Change Due to Reflection “string analogy” graphics from http://dev.physicslab.org/Document.aspx?doctype=3&filename=PhysicalOptics_ThinFilmInterference.xml
- 3. Crest (blue) is reflected as a trough (orange): phase change. Thin Film Interference: Phase Change Due to Reflection graphics from http://dev.physicslab.org/Document.aspx?doctype=3&filename=PhysicalOptics_ThinFilmInterference.xml (good source of self-study material!) n1 n1 n2 > n1 n2 < n1 Crest (blue) is reflected as a crest (orange): no phase change.
- 4. Thin Film Interference: Phase Change Due to Reflection graphics from http://dev.physicslab.org/Document.aspx?doctype=3&filename=PhysicalOptics_ThinFilmInterference.xml (good source of self-study material!) The two cases overlaid: notice how the two reflected waves differ in phase by ½ of a wavelength.
- 5. Thin Film Interference: Phase Change Due to Reflection How to remember the phase change: “Low to high, change is .” (© 2001, D. M Sparlin)