Activities

1. Start with only the red light source on, and showing the interference for red light. With the initial settings for the indices of refraction of the various layers, vary the film thickness to determine which film thicknesses result in constructive interference for the reflected light, and which result in destructive interference for the reflected light. Express these thicknesses in terms of the wavelength of the red light in the film. Do you see a pattern in these two sets of thicknesses?
2. In the limit that the film thickness goes to zero, what kind of interference occurs for the reflected light? How can you explain this?
3. Now, adjust the index of refraction of medium 1 so that it is larger than that of medium 2. Repeat the observations you made in steps 1 and 2 above. What similarities and differences do you observe for your two sets of observations?
4. Find the smallest non-zero film thickness that gives constructive interference for the reflected light when the light is red. Now, make a prediction - when you switch to green light, will the smallest non-zero film thickness that gives constructive interference for green light be larger than, smaller than, or equal to the thickness you found for the red light. Justify your prediction, and then try it to see if you were correct. Repeat the process for blue light.
5. At the left of the simulation, you can see some colored boxes representing the color of the incident light, the reflected light, and the transmitted light. For instance, if you have both red and blue incident light, the incident light would look purple to you, because it is actually red and blue mixed together. With this purple (red and blue, that is) incident light, can you find a film thickness that produces blue reflected light and red transmitted light? If so, how can you explain this?