Question

The default setting is a thin film of glass(n = 1.5) with air (n = 1)on both sides.The starting wavelength is 652 nm and the starting thickness is 544 nm. Use these starting values for this next set of questions.

1. Is there a phase shift on the front (left) interface? On the back (right) interface in the simulation?Justify why there is/isn’t a phase shift at each interface.

2. How does the wavelength in the film (glass) compare to the film in the air? Explain what you observe in the simulation in terms of what you’ve seen in class.

3. Is the interference constructive or destructive? Explain how you can tell from the graphs in the simulation.

4. How many wavelengths are in the glass? How does this (along with the phase shifts at reflection) explain why the interference is constructive or destructive in this case?

Thin Film interference thin film (front) thin film (back) Incident wave before striking film wave in thin film Wave after exiting thin film Vacuum wavelength of incident wave (nm) 652 Wave reflected from front of thin film 1/2 Reflection Shift n of material in front of the thin film 1 n of the thin film 1.5 Wave reflected from back of thin film No Reflection Shift Distance Shift = 2* (thickness) wave reflected off of back of thin film n of material behind the thin film 1 thickness of thin film (nm) 544 Run Pause | Reset Show front reflection on initial wave Combined wave from front and back reflections Show back reflection on initial wave Show Grid

Answer 1

to phare shift. 652 hm 2. 1.5 > g we can see that on the left interface, light is travelling from air (221) glans (1221.5). An, hac ng, there will be a on the right interfere, light is travelling from glans (ng215) to air (nazi). As, ngana, there won't be any phare shaft. wanelength in sa glass, egz ng 434.67 km a la 3. from the graph, reflected from front and back of then film are in phase. Acordingly, the amplitude of combined wave from front and and back reflections is double that the incident wave. Therefore, interference is constructive (waves add The wavelength inside the glans is 1/4 & wavelength. The light undergoes a phare shift of 180 on the left interface. There is no phase shift phase shift on the right interface. The distance travelled the light reflected from the right interface is turne the thickness of glass tab. ie, the path difference of light is at, where 't is thickners. of 4. by 2t: 2x 1/4 suited te 5 ng +2 5 X Condition for both the reys in the same phase 652hm 543.33 ² 5444m Contractive interference actual thicknen. (