1. Thin Films

2. Bright Colors  Colors in nature are not only due to reflected wavelengths. Leaves – spectrum Butterfly – interference  A thin film in on the butterfly’s wings creates the iridescent color.

3. Rebound Phase  Reflection from a fast medium causes no phase shift. High index of refraction to low index of refraction  Reflection from a slow medium causes the phase to invert. Low index of refraction to high index of refractionLow index of refraction to high index of refraction

4. Boundary Effect  At each boundary there are both transmitted and reflected waves.  Like the string there can be a phase shift. Invert from a slow mediumInvert from a slow medium

5. Extra Path  A thin film offers two separate boundaries for light. Initial boundary from air to film – reflection with phase shiftInitial boundary from air to film – reflection with phase shift Second boundary from film to air – reflection without shiftSecond boundary from film to air – reflection without shift

6. Destructive Path  For a perpendicular ray a reflection from the second boundary has an extra path. Length 2dLength 2d  If this is equal to a whole number of wavelengths there will be destructive interference. First wave shiftedFirst wave shifted Shorter wavelength in filmShorter wavelength in film

7. Constructive Too  If the path equals to a half number of wavelengths there will be constructive interference. Second wave matches firstSecond wave matches first  Different wavelengths are enhanced by different thicknesses.

8. Soap Film  Soap film provides different thicknesses to cause different wavelength to undergo interference.

9. Newton’s Rings  Air or water between glass can also act as a thin film. Different index of refractionDifferent index of refraction next