1. Interference... The physics of thin films and more...

2. Wave Superposition and Interference What happens when waves meet? Path Difference - Phase Difference

3. The Physics of Thin Films A Phase difference can occur because of… –path differences for different combining wavetrains –phase shifts introduced under certain reflections –go to applet thin filmthin film

4. Single, Double and Multi-Slit Interfence Simple Case: Assume each slit acts as a single source simulate this… –diffraction of water wavesdiffraction of water waves –thin slit diffractionthin slit diffraction The Grating Equation:

5. Structural Colour in Plants and Animals The iridescent sheen of a bluebird wing or the extravagant colours of many butterflies and moths arise - not from chemistry (pigments) but from physics (interference effects)!!

6. The Physics of Structural Colour Light reflects from slightly different places along the surface. An optical path difference is introduced

7. Some colours work - some don’t... The optical path difference  is just the extra distance that one ray travels wrt to an adjacent one. It’s easy to see that this leads to: for constructive interference