How do oil spills/spots (i.e. in parking lots and streets) create rainbows?

Lou Bloomfield Leave a comment

How do oil spills/spots (i.e. in parking lots and streets) create rainbows?

A thin layer of oil on water creates interference effects, just like those seen in a thin soap film. Sunlight reflects from both the top and the bottom of the oil layer and these two reflections can interfere with one another. If the blue/green wavelengths of light interfere destructively on their way to your eye, you will see the oil layer as red. If the green/red wavelengths of light interfere destructively, you will see the oil layer as blue. How you see the oil layer depends on its thickness and the angles of the light.

Does red or blue light bend more in glass?

Lou Bloomfield Leave a comment

Does red or blue light bend more in glass?

Blue light almost always bends more than red light because blue light almost always travels more slowly through glass than does red light. This phenomenon is known as dispersion However, there are some glasses that exhibit anomalous dispersion, where red light travels faster and bends more than blue light. Anomalous dispersion only occurs when there is a resonant absorption of light in the glass, typically because of some impurity atoms or ions in the glass or because of some transition that occurs in the glass itself. While the resonance will only absorb light at one particular wavelength, it alters the propagation of light at nearby wavelengths. At wavelengths just shorter than the absorbed wavelength, light travels anomalously fast through the glass so that it bends less than light that is somewhat redder in color.

Does air pollution contribute to the blueness of the sky (make it bluer)? Has th…

Lou Bloomfield Leave a comment

Does air pollution contribute to the blueness of the sky (make it bluer)? Has the sky become more blue with the advent of technology (factories, machinery, etc.)?

Yes. Pollution does tend to make the sky bluer and the sunsets redder. However, pollution also imparts colors directly by absorbing certain wavelengths of light. The orange haze that hovers over cities is often caused by nitrogen oxides, which are simply orange in color and act like pigments to make everything appear orangish. However smoke and dust certainly change the look of the sky by increasing scattering. Natural disasters are even more effective: volcanic eruptions create the most beautiful sunsets of all by tossing vast amounts of dust into the air.

Does a mirage operate under the same principle as the puddles on a road?

Lou Bloomfield Leave a comment

Does a mirage operate under the same principle as the puddles on a road?

Not exactly. A puddle contains water, which reflects light directly. Light from the blue sky travels toward the puddle and illuminates it. As the light enters the water, with its higher refractive index, part of the light reflects. You see this light when you look at the surface of a puddle. But a mirage involves refraction (bending) of light. As light from the blue sky enters a regions of hot air near the surface, that light bends upward. You again see light from the sky, but bent upward by the air rather than being reflected upward by a surface of water. Since the two appear similar, you interpret the shimmering blue light of a mirage as coming from a pool of water. But it is just hot air.

As long as the sun is to our back, shouldn’t the rainbow stay visible; instead o…

Lou Bloomfield Leave a comment

As long as the sun is to our back, shouldn’t the rainbow stay visible; instead of disappearing when we approach it?

If the sky were uniformly filled with water droplets and uniformly illuminated with sunlight, then you would always see the rainbow, no matter where you moved. However it would always appear out in the distance. The light that reaches your eyes as the rainbow comes from a broad range of distances, but it appears to come from pretty far away. As you walked toward this perceived rainbow, you would begin to see light from other raindrops, still farther away. You could never actually “reach” the rainbow. It would just move about with you; always appearing to be in the distance.

You said an ice cube will not get hot in the microwave because the molecules won…

Lou Bloomfield Leave a comment

You said an ice cube will not get hot in the microwave because the molecules won’t “flip”. If this is so, then why do frozen foods cook in the microwave?

As noted previously, the water molecules in frozen foods are not all bound up perfectly inside ice crystals. As long as there are a few relatively mobile water molecules, even frozen food will eventually absorb enough energy to melt. Once that happens, the food can cook easily. Of course, the melting process is frequently very non-uniform so that food comes out with hot and cold regions. In general, frozen food cooked in a microwave is not very satisfying.

Why do some microwave ovens not seem to have a metal surface in the cooking area…

Lou Bloomfield Leave a comment

Why do some microwave ovens not seem to have a metal surface in the cooking area?

The cooking chamber of a microwave oven is always metallic. Even the glass door has a metal grid across it to keep the microwaves inside. This metal chamber may be coated with paint or plastic but it is there nonetheless. Without it, the microwaves would leak out and the oven would be hazardous and inefficient. It would cook objects throughout the kitchen.