Gasoline falling on the wet street
After the rain, the asphalt streets were wet in the sunlight, often seen here and there with colorful oil spills. If you look closely for a while, you will find that gasoline drops are falling from passing cars. How do all kinds of colors appear when gasoline falls on the water?
Gasoline is lighter than water, falls into the water and spills out, floats on the water’s surface, forming a thin oil film. Although the oil film is extremely thin, it looks like a transparent cellophane sheet, also on the front and back. When the sun shines on the oil film from the front, encountering the back of the oil film sticking to the surface of the water, it is immediately reflected again. The reflected light rays back to the front of the oil film will again cause some reflection. The reflected light reflected back and forth inside the oil film, like a ping-pong ball thrown back and forth between two parallel flat plates.
Sunlight comes from seven types of light: red, orange, yellow, green, blue, indigo, and purple. When it is reflected back and forth between the front and back of the oil film due to the very small distance between the two planes, the two light beams from the front and back, respectively, bounce off each other, which can be piled up. So the seven kinds of light in the sun, where the thickness is different, the color will be strengthened, the color is weakened, even annihilated each other. The state is that some show a little red on the oil film, some a little green, some show a different color, so the oil film looks colorful. This type of color is called thin film. Such a phenomenon is called interference of light.
It is not just oil films that can cause interference of light. As long as a light shines on any transparent thin film, this can happen. For example, soap bubbles, dragonfly wings or fly wings, CDs, etc., under the sun’s irradiation, all reveal many colors, all caused by interference of light.