Abstract Thursday: Rainbow Patterns

I didn't have to go far this morning to get my Abstract Thursday blip (there's no theme this week). On the road just round the corner was this rather pretty example of the rainbow effect of a thin film of oil on the wet road: I liked this particular portion of it which I thought resembled multi-coloured flames.

Physics Lesson (Sorry, I can't help myself, I love to know how things happen. Please ignore this if you don't like physics or if you prefer to think this effect is magic!): The explanation for the separation of the various colours of light is different from what happens in water droplets in a rainbow. If the thickness of the oil film is about a quarter of the wavelength of light (which itself is between 0.0004 to 0.0007 mm - quite small!), then rays of light reflected from the top of the film interfere with those reflected from the bottom of the film, either boosting or cancelling one another out. The extent of this inteference varies slightly depending on the exact wavelength of the light (and therefore its colour) and also varies according to the thickness of the oil film and the angle at which the light rays strike the oil. Hence in some areas one particular colour of light is boosted or cancelled, and in other areas different colours experience this effect. (There's a fuller explanation, with diagrams, here.)

Many thanks as always to Ingeborg for hosting Abstract Thursday.