- 3,750
- 1,832
- Homework Statement
- This isn't actually homework - but it's like homework and I am not completely certain about the full answer. Most importantly, I believe it's entertaining.
The statement is this: They have just repaved the parking lot in back of my work place. As I look down on the fresh asphalt from a 2nd floor corridor, I see a sheen - wide bands of rainbow-like colors. Each of these bands is about a meter wide and a full cycle of colors is seen about every 4 meters. The corridor is lined with plate glass panes, each about 2 meters wide. As I walk down the corridor, the color pattern on the pavement stays fixed to positions on the pavement until I cross to the next pane. Then it shifts as I cross to that next pane. So, for example, from one pane, I see the purple ban lined up with a particular fire hydrant. As I continue walking across that pane, the purple ban remains in that exact position. But when cross the divider between panes, the view through the next pane shows the pattern shifted and now the hydrant is lined up with a yellow ban.
Explain this affect.
- Relevant Equations
- This is a word problem. I believe it can be answered without resorting to equations.
This problem is two parts. The first is to determine what effects are being provided by each of the elements - 1) the window panes; 2) the asphalt surface. My answer to that is
The second part of the problem is exactly why you get this affect.
And one more spoiler:
Each pane is polarizing light at a somewhat different angle. And: As you move across the asphalt surface, the oil thickness will change - and the resulting constructive and destructive interference will affect different color wavelengths differently.
The second part of the problem is exactly why you get this affect.
Clearly, the oily layer affects both the interference and polarization based on the wavelength. But I imagine there must be some easy way of describing why the polarization is not only color-dependent, but also has the affect of rotating the color phases of the sheen.
And one more spoiler:
One of the panes does not show the sheen at all. Or, at least, not that I could notice. Compared to the others, its like looking at a black and white photo.